Mainship 34 models

[timjet]

I am in the market for a used trawler/motor yacht and the early 80's 34 Mainship seems like an economical option. As described by Jack Horner in Boat US, Mainship built 3 models of the 34, Mark I, II, and III. Does anyone know the history of these models. According to Mr. Horner the Mark III had the most desirable Cabin/Cockpit characteristics. In looking over used boats on the internet, I can't determine when the Mark III was first built. It was my understanding Mainship ceased production of the I and II when the III was built.
Any information would be appreciated.
Tim

 

[Baker]

I have shopped these boats extensively. The mk1 is the most "trawler like". I prefer it since it has the cover over the aft cockpit...it is practical and it just looks better. The Mk2 seemed to be aimed at more of the sportfish market. The cockpit was bigger and the saloon was smaller. I think they missed the mark as this was the least popular of the bunch. The came back with the mk3 which lengthened the saloon at the expense of cockpit space....still looks like a sportfish to me....nnothing wrong with that if you like that sorta thing. The hulls are all the same. The hull design was done by Cherubini...made to be easily driven thru the water. Anyway, the later the model, the more likely you would get the 200hp engine(Perkins 6-354). The 160hp engine wasw more likely on the older models. It is just 40hp but it is truly the difference between cruising at 12kts or at 8kts. That 40hp gets it over the hump. If speed is important, make sure you get one with the 200hp motor. Many have actually been repowered so look out for that as well. They also had soft deck issues. They have been around so long that most have been repaired but this is something that definitely needs to be looked at. They are a TREMENDOUS value and would make a great cruiser for a couple.

Good luck and lemme know if you have any other questions....not like I could answer them....

 

[timjet]

John,

Thanks for taking the time to discuss the Mainship 34. Your comments made me re-look the different models. It appears the mark I has by far the largest fly bridge. The other two have very small fly bridges and would not suit my purpose.
I also noticed the later models have a lighter wood, perhaps oak or mable in the interior vs the dark teak of the older models.

My wife fell in love with the Mainship 35/39 after viewing one at a marina we were overnighting at. We both particularly like the steps leading to the fly bridge vs the ladder in many of the '80 vintage boats. Too bad we can't afford one.

Mainship did not seem to make many smaller diesal trawlers/motor yachts after '85. It seems they switched to gas until the 35/39 dayviewed in about '97.

I must sell my sailboat before I get serious about a trawler. At the rate boats are moving the Mainship 35/39 may well fall into my price range by the time I'm ready to buy.

Is it easy to spot the soft deck issues you mentioned?

Tim

 

[Baker]

Yes it is. And a good surveyor would not miss them either. I will echo your sentiment about the 35/39. Great looking boat and great layout. We love those boats. And can't afford them either. They have managed to retain their value quite well.

 

[Nomad Willy]

John,
The old Mainship 34 caught my eye When I was shoping for a cruiser before Willy. I liked the narrow bow and the overall looks of the boat. I assumed they burned 3 or 4 gph and was mussing about how I could afford that when I saw one out of the water. The hull dos'nt reach it's maximum beam untill it reaches the transom and at that point it's still getting wider. The hull is warped (going from deep V fwd tward flat as one moves aft) all the way to the transom. At 12 to 18 knots this should be extreemly efficent and that is, of course extreemly desirable. But I decided it would be like a bear in a greased pit in following seas so I wrote them off. Iv'e talked to several owners since then and all confirmed that following seas is not a good place to be in a Mainship 34. Lately though Iv'e thought I may have written the boat off prematurely as the problem in following seas may may be slight and one can frequently make things better with course changes. My own Willard isn't perfect in following seas either (its very full aft)* but if I keep the 100 gal water tanks full in the lazerette the big rudder takes care of me. A true doubble ender is slender aft as well as fwd. Anyway I'd be interested to know what you mainship owners think and if your hull John is like the MS 34.

Eric Henning

 

[Baker]

Anything with a wide square ass is gonna give you the characteristics you speak of. It is just a matter of having too much buoyancy aft. BUT, if you can "outrun" the wave train, this is not as much of an issue...ie get up on plane. You still aren't outta the woods there either. As you come off the top of a wave, the bow can potentially dig in and almost broach if you do not have the boat trimmed properly. Anyway, the hull of my boat is similar to what you describe and is basically the posterchild of a semi-planing hull. FWIW, Cherubini is the designer of the MS 34 motorcruiser.

 

[albin man]

confirmed that following seas is not a good place to be in a Mainship 34

I ran one for 14 years and that is only true for the low powered, low speed ones. Anyone that has been repowered or came with 220 or more hp can run fast enought that this is usually not an issue, esp if you have a decent autopilot, which all slow boats should have IMO.
These hulls will run great up to 16 knots then they get squirelly as they start to chine walk over 16.
AM

 

[Baker]

Just reading thru this thread again. And Albin man, it really isn't "chine walking". All semi-planing hulls will do what you are saying. What is happening is that the only portion of the hull that creates lift is the aft portion. The faster you go, the more lift is created....common sense. It does get to a point where the aft end of the boat creates enough lift that the front end starts to dig in....or in reality it is "bow steering"....and it is a very odd feeling. Anyway, my current boat, the Pilot 30, comes with 2 different engine options. A smaller one(240hp) and a bigger one(315hp). I have the smaller one and it is just powerful enough to get you into this regime(about 17 or 18kts). But the boats with the larger engine can easily get into that regime so ultimately you are paying for all that extra engine and not really putting it to use. You may be able to cruise at 16 a little easier whereas my boats happy spot is 15kts(240hp).

Anyway....FWIW

 

[albin man]

After discussing this phenomena with one of the original Mainship 34 engineers, he described it as*"chine walking", I did not come up with that terminology.
One very slight turn either side and the side of the keel would then become ther lifting part of the hull. Turn the wheel and it would flip to the other side.
(I never experienced that on any other semi planing down east hull even at 30 knots.)
He said it was "possible" to prevent it by adding some spray rails to each side at the waterline but I decided not to go thru that much work since the engine was at max cruise rpm when I was at 15.5 knots.
The only time I went over that was to run the boat up to WOT (18.5 kt) at the end of some cruising days to make sure all systems were up to snuff.

 

[Marin]

The little 17 or 18 foot SeaSport that we used to take the cover photo for the Kenmore book chine-walked horribly. It would run along tilted to one side and then without warning or reason flop over to run tilted to the other side for a few minutes, and then it would flop back. This was on a full plane in barely rippled water. The boat was too small to warrant the expense of trim tabs which might have dealt the problem. But we were told that this is the characteristic of this particular model of SeaSport. Hull too short for its configuration and speed? I don't know. But it was really annoying and Kenmore finally got rid of the boat.

-- Edited by Marin on Tuesday 7th of September 2010 02:28:04 PM

 

[Baker]

albin man wrote:


(I never experienced that on any other semi planing down east hull even at 30 knots.)

Just curious what semi-planing hulls do 30kts? *"Chine walk" I think is more of a general term. * *BUT, I am pretty sure that chine walking is when the boat bounces from chine to chine while on plane at fairly high rates of speed. *Not while doing 15kts on a 16,000lb boat...

*

My example in my previous post may be a description of chine walking....but I seriously doubt it. *And it is likely the same phenomenon that I experience in my Mainship Pilot....and the same that was described in this thread ref the Mainship 34....which I don't believe to be chine walking. *I don't know if there is a term but I do think my description of the dynamics of it are what I explained above. *If that is chine walking, so be it.


-- Edited by Baker on Tuesday 7th of September 2010 03:34:29 PM

 

[Codger2]

Baker wrote:"BUT, I am pretty sure that chine walking is when the boat bounces from chine to chine while on plane at fairly high rates of speed."*

I agree! That's the definition of "chine walking."

*

 

[albin man]

"Just curious what semi-planing hulls do 30kts?"

Been on a few downeasters with lots of power

"Chine walk" I think is more of a general term. * *BUT, I am pretty sure that chine walking is when the boat bounces from chine to chine while on plane at fairly high rates of speed. *Not while doing 15kts on a 16,000lb boat..."

Sorry, this is exactly what happens to*this 20,000 lb boat at 16 + knots. This happens to every old 34 Mainship that has been re-powered up enough to*reach 16 knots.

*

*

 

[Baker]

Search chine walking on you tube and you will see what it is. Chine walking is downright frightening... the phenomenon we are talking about with Mainships is not.

And as designers wish to get more speed out of a design, they have a tendency to go more towards a planing hull. *It would be senseless to design a "small" boat to go fast using a semi-planing hull. *I guess all I am saying is that it is not black and white. *And there may be a chance these "Down Easters" are more of a modified V than semi.... *Like those Downeast Eastbays. *Not semi Planing. *I think they boast a Ray Hunt designed modified V. and do go your stated 30kts+....not the same animal. *They aren't stupid over at Grand Banks. *In fact, the newest models of Grand Banks "Trawlers"(Heritage series) are now all modified V....why...because the market wanted speed. *So GB did the proper thing...they designed a proper hull for speed. *The improper thing would have been to overpower a semi planing hull.


-- Edited by Baker on Wednesday 8th of September 2010 09:55:38 AM

 

[Marin]

Baker wrote:And there may be a chance these "Down Easters" are more of a modified V than semi.... *Like those Downeast Eastbays. *Not semi Planing.*

Based on the lobsterboats I've seen out of the water I would tend to agree with John.* they are planing hulls with a keel.* And some of them have the power to get on a plane although I suspect most of them don't.* So while they tend to mush around like a semi-planing boat it wouldn't take much more to get them on a full plane.* In a true semi-planing hull like our GB, we'd need a GE90 hooked to the Velvet Drives to get the thing onto a full plane at which point I suspect it would be so unstable as to be dangerous.

An Eastbay has a hull somewhat similar to the hulls used on WWII PT boats, which were fully planing boats.

Here's a couple of shots I've posted before of a new lobsterboat.* Also the basic drawings for an Eastbay.





*

 

[Baker]

Don't have time to reply Marin but I would say that Lobster boat looks semi to me. Look at the difference between that and the Eastbay cross section. Semi boats have no lifting area forward and then flatten out(very flat) aft. The modified V never fully flattens out but it does produce lift along the full length of the hull....
Anyway, unfinished and will finish later after dinner.

 

[Marin]

If you look at the bottoms of the racing hydroplanes of the 1930s (Hackers, Gar Woods, etc) they look pretty much like the lobsterboat bottoms except they don't have a keel of course. In a planing boat, the hydrodynamic pressure is what lifts the hull out of the water to reduce drag, and the flatter the bottom the more hydrodynamic pressure there will be. The only reason to stick a Vee down there is to keep your teeth from pounding out. On a plane the whole front part of a lobsterboat-type hull is going to be out of the water or almost out of the water anyway. It all depends on how fast the deep forefoot (which is there to cut the water) flattens out as to how efficiently the hull will plane.

A Vee hull, or even a semi-vee hull is not an efficient planing form. This is why you have to put so much power in them to achieve a full plane. But.... a deep V or semi-V gives a much nicer ride which is pretty important to most folks. They will happily burn more fuel to not get pounded to death.

A good example is our 17' Arima and an equivelent Bayliner runabout. Our Arima's hull has a very deep forefoot to cut the choppy water in this area but the hull then flattens out very fast to almost totally flat at the transom.* If you cut the keel off a lobsterboat hull,*what you're left with is almost identical to the*bottom configuration of our Arima. *It will plane very nicely with as little as 50 hp on it although the most common power for this model is 90. The equivelent-sized Bayliner runabout has much more of a Vee bottom because this give a much nicer ride than our Arima, but it takes a fair amount more power to plane it at the same speed we go with 90 hp. The Bayliners are usually 125-150 hp.

I mentioned the WWII PT boats which were fully-planing boats.* While their forefoot was not as deep as one gets with a lobsterboat, the hulls flattened out pretty fast and at the transom*were a very shallow Vee. This was to generate as much hydrodynamic pressure as possible to lift a heavy, 80'*hull out of the water as far as possible.* Their hulls retained a degree of Vee to them because*of the rough conditions they were called to operate at at speed.** But at the transom their hulls were flatter than the Eastbays.* The top sustainable speed of an 80'*Elco PT was 45 mph (when new).* And they did it with "only" 3,600 horsepower which is not all that much considering the size and weight of the fully armed boat.


-- Edited by Marin on Wednesday 8th of September 2010 04:32:26 PM

 

[Baker]

Look at that lobster boat hull. It has a VERY deep forefoot and then it continuously flattens out as you go aft....very flat....like straight as a board flat. that is basically the poster child of what a semi- planing hull is. The idea is that the front part of the boat will cut through the weather while the aft end provides enough lift to get you some speed. This will always be a compromise and my reasoning for asking Albin Man about his "30kt semi boats". I am still skeptical about a semi displacement(planing) boat that will do 30 kts. It is either a poor design(execution) or a very large boat(read crew or utility boat here). Crew boats tend to be very large(ie 100ft) and semi planing and very highly powered(read triple 2000hp Detroits here). Their purpose is sea keeping ability......certainly not efficiency!!!!

Now, let's get back to the dynamics of it. Look at that hull shape. There is nothing providing lift for the front half of the boat. And the aft half of the boat provides a lot of lift. The faster you go, the more the aft end of the boat lifts up. It will get to the point where the aft end of the boat is higher than the forefoot and the bow begins to steer the boat.....you can take it a step further and deduce that the rudder is blocked out by the whole front end of the boat. This phenomenon is further aggravated by the downward pitch caused by the standard set up of the propshaft....ie the downward angle of the propshaft causes the boat to pitch down as power is increased. THIS IS NOT CHINE WALKING!!!! If you have to put a name on it you could call it "BOW STEERING". In effect, it is somewhat of a broach that you would experience on a sailboat...without the wave/sail causing the bow to dig in.

To summarize....the reason to put enough power for a semi planing boat to plane is sea keeping ability. The front half of the boat cuts through the weather while the aft half provides enough lift to plane. Like I said above, this is a compromise. An absolutely FLAT bottom boat would be the most efficient assuming the water would be perfect glass. A modified V small boat will pound into the weather...but it is more efficient than a semi boat. A semi planing boat is NOT efficient. It is a better sea boat than a planing boat. The reason they put semi planing hulls on boats that are NOT powered enough to plane is "static stability"....that is their initial stability when they are "upset". The extra flotation provided by a hard chine makes them resistant to roll....INITIALLY.

Show me a 30kt semi planing boat and I will show you a very poorly designed/executed boat....unless it is "relatively" large. Again, the only reason for powering a semiplaning boat to plane is sea keeping ability....PERIOD!....there are compromises and efficiency is one of them....as is this bow steering phenomenon!!!!

-- Edited by Baker on Thursday 9th of September 2010 12:18:40 AM

 

[Marin]

Baker wrote:

Look at that lobster boat hull. It has a VERY deep forefoot and then it continuously flattens out as you go aft....very flat....like straight as a board flat. that is basically the poster child of what a semi- planing hull is. The idea is that the front part of the boat will cut through the weather while the aft end provides enough lift to get you some speed.

The flatter, lift producing section of the hull extends farther forward than you would think.* The lobsterboat hull planes very nicely if there's enough power in it.* Not all of them, or perhaps not most of them, have this much power because of the cost.* But we watched a newish*commercial lobsterboat leave a harbor on PEI and immediatly accelerate to a full-bore plane.* The forefoot and forebody were totally out of the water.* The thing basically looked like a ski-boat on the plane.* PEI lobsterboats are all 46 feet (I think) long.* Maybe it's 45 feet or 47*but whatever it is it's one foot less than the length when a different kind of operating certificate or tax or something kicks in.*

This particular boat was not carrying any pots but going out to pick pots it had set earlier so it was traveling light except for bait.* God only knows what it had for an engine, but it was moving fast and appeared totally stable.* The boat had the same hull configuration as every other PEI lobsterboat we saw, in or out of the water (see photo).* Deep forefoot rapidly*V-ing out to a nearly flat bottom for the aft two-thirds of the hull or so, plus the faired-in keel.

So flat or flat-ish bottom is not automatically*part of the definition of a semi-planing boat.

*


-- Edited by Marin on Thursday 9th of September 2010 07:23:06 PM

 

[jleonard]

"Show me a 30kt semi planing boat and I will show you a very poorly designed/executed boat....unless it is "relatively" large. "


One*boat I was on several times that could make that speed was actually a 35 Duffy center console with a big two*stroke *Detroit. Built to get to the tuna grounds fast. The boat was very confortable at high speed if the seas were flat however the owner didn't care much if it snotted up he would still pound thru it. Knock your fillings out for sure.
But* if he throttled back to 16/17 or thereabouts it would slice thru the snot like silk.

 

[Baker]

Marin wrote:

*

So flat or flat-ish bottom is not automatically*part of the definition of a semi-planing boat.

*


-- Edited by Marin on Thursday 9th of September 2010 07:23:06 PM
*

No it isn't...not at all. *BUT.....Semi planing to me(ignorant) is a hull that does not produce lift over ALL of its area(hence the term). *The front half does not produce any lift at all. *The aft half does. *Now to get the boat onto plane with some semblance of speed/efficiency, a lot of lift "lost" on the front half has to be regained in the aft lifting sections. *As you stated and as most of us know, the flatter it is, the more lift it provides. *And most semi planing hulls flatten out significantly aft whereas a modified V generates lift over the entire wetted area so they carry a lot of V all the way aft(deadrise). *Modern V hulls are more effiicent and more stable at higher speeds but they do tend to pound into the weather. *Whereas a semi planing hull sacrafices speed and efficiency but the do "slice thru the snot" better....as Albin Man put it. *Because of this, they also have a tendency to be wetter since they are going THROUGH the weather instead of over it.

EDIT:


But, now that I think about it(ignorantly), if you did carry a lot of deadrise in a Semi boat that instability we have been talking about would be greatly exaggerated. *In other words, I will go back and somewhat disagree with your above quoted statement. *Semi planing boats need to have "flat as a board" aft sections not only to increase lift/speed/efficiency, but also for stability purposes. *Too much V aft and the thing would just flop over to one side....not to mention the speed/efficiency that would be lost.

*




-- Edited by Baker on Friday 10th of September 2010 01:55:01 PM

 

[Codger2]

Baker wrote:" Too much V aft and the thing would just flop over to one side....not to mention the speed/efficiency that would be lost."

Doesn't dihedral or anhedral have the same effect on an aircraft as deadrise has on a boat? The result being "Stability" in both cases?

*

 

[Marin]

Baker wrote:Semi planing to me(ignorant) is a hull that does not produce lift over ALL of its area(hence the term).

Your definition is not the one I've read in articles by marine architects like Tom Fexas.* They use the term semi-planing to refer to a boat that is incapable of achieving a full plane unless almost unachievable amounts of power are available.

I've never seen these guys refer to a planing hull as being one that can develop lift, or significant lift, over the entire wetted surface.* In fact I've never seen any of the terms--- planing, semi-planing, semi-displacement, or displacement--- related to how much of the hull area produced lift (or didn't produce lift in the case of the displacement boat).**They are related to how much lift is generated, but not how much of the hull's area is generating that lift.* At least not the way I've seen it written about.

A semi-planing hull, by guys like Fexas' definition, is one that uses speed and hull shape to achieve a degree of hydrodynamic lift that will at least begin to lift the hull and reduce drag.

Fexas has designed some fully-planing hulls that, other than a much more raked-back stem, have bottom configurations exactly like commercial lobsterboats--- Vee in the front, flat in the back.* He's also designed fully-planing hulls that are deep-V in shape all the way back*(and have massive powerplants).


If you take the keel off a Grand Banks*hull you'll have*a halfway decent planing*hull if you put sufficient power in it.* I say halfway decent because even without the keel, it's not an efficient design for a fully-planing*hull.* But the keel and the*fairing into it*adds a massive amount of*drag, thus rendering* the hull*"semi-planing" because there's no way you'll get it*onto a full plane with the kind of power typically used in recreational boats.

 

[Marin]

SeaHorse II wrote:


Baker wrote:" Too much V aft and the thing would just flop over to one side....not to mention the speed/efficiency that would be lost."

Doesn't dihedral or anhedral have the same effect on an aircraft as deadrise has on a boat? The result being "Stability" in both cases?

*

I would say yes.* If you look at the back end of some deep-V hulls they are almost as "veed" at the transom as they are*much farther forward.* This makes for a smoother ride, and yes, it would add stability, at least while underway.

*

 

[Marin]

Baker wrote:

*Modern V hulls are more effiicent and more stable at higher speeds but they do tend to pound into the weather.

I'll give you the "stable" part but not the "efficient" part.** A V-hull is less efficient in terms of the amount of power*it takes to plane it than a flatter hull.* As I described earlier, this was a conscious compromise by Mr. Arima in the hull design of his very popular trailerable fishing boats, and is also apparent in the C-Dory.* In these two boats, it was all about efficiency and needing less power to plane (which kept purchase and operating costs down).* So Arima designed a hull specifically for PNW waters which can be rather choppy even on nice days due to tide rips and such, but also provided the ability to go fast with relatively little power.* The resulting hull has a very deep forefoot to deal with the chop and a very flat mid and afterbody to make it plane with little power.

A V-hull takes more power to plane because its hull shape is less efficient at producing hull-lifting hydrodynamic force (the force is angled in due to the angle of the bottom as opposed to straight up as is the case with a flat-bottom boat.)* So for a given speed*you need to generate more hydrodynamic pressure against the V-bottom for a boat of a given weight than you would with the same size and weight of boat with a flat bottom.* Which takes more power to do.

Not sure all that made sense but the bottom line is that a V-bottom is a less-efficient planing configuration than a flatter bottom but it gives a much easier ride.

*


-- Edited by Marin on Friday 10th of September 2010 04:30:56 PM

 

[Baker]

We are getting into semantics here Marin like we always do. The reason why your marine architects define it as a hull "that does not achieve full plane" is because they do no develop as much lift as a planing hull...simple as that. Now I stated the reason why they don't above. I am in full agreement with their definition...I just went a little further as to the "why" of it.

As far as dihedral goes and how it relates to this....well it doesn't really. There is alot more going on in an airplane(ie other lifting and stabilizing surfaces). I will go further to say that the entire hull of an airplane is immersed in the fluid and every single inch of it's surface has a dynamic effect on the whole operation. So it is a crude comparison and one I don't think really applies.

A V hull has dynamic pressure along the full length of the wetted area...IOW, lift is created basically along the full length of the hull. The forward part of a semi boat is basically a full displacement hullform. It does not create enough(if any) hydrodynamic pressure to provide stability. To counter that lack of stability forward, you need more aft. If you had too much deadrise aft, it would suffer stability issues. Trim tabs might help but I think you would need more than that....strakes and such.

Marin, my point about efficiency ref V hulls was one of comparison. A v-hull is more efficient than a semi hull. Everybody knows that a flatter hull is more efficient. Are you trying to tell me that Mr. Arima is hiding some magical semi planing hull design that he has never sprung on the marine world? I am thinking it is more a "negative economies of scale" thing...ie something you can get away with on a smaller hull that won't translate well into a larger one. There is nothing magical about your Arima hull....however sweet it may be.

The spectrum would be:

A flat bottom skiff on one end with a sailboat hullform on the other with a semi planing hullform right in between. Now you know as well as I do that we can build a boat anywhere along that spectrum. ANd as it relates to efficiency on plane, that flat bottom boat is the most efficient and they become less efficient as you go towards the sail boat....ON PLANE!

Gotta go....wife wants me off this thing and I don't blame her....beautiful, although hot, day down here in Tejas!!! Y'all have a great day.

 

[Marin]

Baker wrote:

Are you trying to tell me that Mr. Arima is hiding some magical semi planing hull design that he has never sprung on the marine world?

An Arima is a fully planing hull, not a semi-planing hull.* What I'm saying is that the flatter the bottom of a fully-planing hull is, the more efficient it will be.* However the ride will suck as the water gets rougher.* It sounded like you were saying that a V-bottom on a planing boat is more efficient than a flat bottom on a planing boat.* It's the other way round.* What Arima did is create a boat that was, in his opinon, the optimum compromise for our local waters between very efficient planing and a halfway decent ride.* So his boats have a deep-V forefoot that rapidly flattens out as you go aft.* Nothing semi-planing about it.

Here's a not-so-great shot of Malolo on its trailer.* Nothing magic about it's design, it's just one of the more successful hull-shapes for this type of boat.* At cruise rpm (not full throttle) Malolo goes 30 mph with 90hp.* If the hull was a deeper V all the way back, like a Grady-White or something, the ride would be way nicer in choppy water but it would take a lot more power to achieve the same speed for the same size and weight of boat.



*


-- Edited by Marin on Sunday 12th of September 2010 01:24:41 PM

 

[Nomad Willy]

About Baker's idea about lift here and no lift there * * ..any part of the hull that is acting on the water passing under it that is at some angle of attack is (would be) creating lift. But also any part of the hull that is decreasing in deadrise as the water goes aft will also produce lift.Consider the M 34. It's deadrise decreases constantly all the way to the transom. So the M34 would be creating lift over it's entire bottom when the keel is running level. Most or at least many boats have constant deadrise from amidships to the transom or from a point 1/4 of the way fwd back to the transom. Of course at mid planing speeds down to almost disp speeds there will be considerable angle of attack and lift will be over the entire hull in contact w the water. Of course any part of the hull not in the water will not be creating lift from the water. Many people think that a planing hull will have a nice soft ride if it has a nice pointy bow. Not so. Planing hulls ride on their bottoms * *..not their bows.*While quartering a following sea the aft corner of a hull like the M 34 sticks out to meet the wave and contacts it before it would if there was plenty of deadrise or if the boat was a double ender or even if it were flat. So the wave pushes the windward corner up prematurely and since there is little buoyancy to counter act that force, some aft but very very little fwd the boat rolls w it's lee rail down. If the boat is wide and full at the chines fwd (like a Uniflite, an Island Gypsy or a 43 Albin the boats rolling toward the trough is arrsted. If the seas contact the port stern corner first lots of port rudder will help roll the boat into the rushing sea and away from the trough.

 

[Andy G]

I have been trying to follow this post, but with my limited grasp of the finer points that John,Eric & Marin decend/ascend to I a am a little lost.

As I just happen to have some shots of the underside of our IG36 I am putting them up as I am of a more visual than theoretical leaning.

To me the aft of the IG looks pretty flat once it is fared away(?) from the keel,she looks to me a little like the lobster boats photos.

Am I right in thinking that in a following sea then, and given the small rudder area, she is more susepetable to broaching than say a bilge keel configeration?

 

[Moonstruck]

I have owned and run planing boats with sharp entry and 12 degree deadrise aft, 24 degree deep V to the transom, and 16 degree deadrise to the transom.* They do not pound into a head sea.* The deeper the deadrise the more stable they are in a following sea.* Without dynamic lift from speed, they will roll almost like a round bottom.* At speed they have a tendency which increases with deadrise to lean into the wind.* That is why trim tabs are needed on a deep vee.* Tabs also help trim angle.* Too much bow down and the boat*gets squirlly.* In a big following sea take the tabs off to sink the stern down for stability.* The deeper the Vee the more power to keep it up on plane.

My Mainship 34 Pilot was good in a head sea.* Squirlly in a following sea, and wet until I added smart rails to deflect spray.* It was a full keel lobster styled hull that would cruise 17 knots with a 370 hp Yanmar.* All in all it was a good cruising boat.