Powertrain choices

[Nomad Willy]

Bob I don't think Ferrari built a rear engined car. But they did build mid engined cars that were very well balanced. The engine was ahead of the rear axle.

Still I don't think any car maker made a success of a rear engine car except VW and they saw the light eventually.

As to boats w IO drives in the stern one could attempt to balance the boat by putting things far fwd. Not much else heavy except people and if you put them far fwd the'll have a very rough ride and the waves will be pounding on the bottom of the center of the boat where nothing is and the weight at either end will be constantly trying to break the boat in half so it will need to be strong. Just more unnecessary weight.

 

[rjtrane]

Your right. VW finally saw the the light. In 2013! After ONLY 1.5 Million Kombis (the classic VW bus), VW in Brazil is admitting defeat of the rear engine vehicle after ONLY 53 years in production.

I hate to say your prejudices are showing. A naval architect designs a boat, he actually spends time allocating the weights fore and aft and if a boat has the motor aft , designs the hull for that weight in that location.

Good design dictates that liquids are located near the fore and aft center of buoyancy so as water and fuel are used, trim remains the same. The engine is a fixed weight and can be allowed for in the design with other fixed weights balancing as necessary.

Since the vast majority of inboards are I/Os, it's hard to think they're all bad or poorly designed boats. You may really like you motor in the center of the boat. You may also like blondes. That's not to say redheads are diminished.

BTW, taking your car analogy further , most private planes have their motors in the bow. Should we therefore conclude that boats would be better with motors and props in the bow ?

 

[Andy G]

Bob,
VW, Corvair, Tucker.

"Don't know about the Italian things but all rear engined cars seem to be a failure except the Porsche. And being German it dosn't need to be a design success."

Eric, I don't know what criterion you are using to describe the VW Beetle as a failure, they sold about 17 million cars worldwide, and had a production run of over 30 years.

They fitted their design/cost specification probably more effectively, than any other car ever manufactured, although you could put up an argument in favour of the Ford model T.

They managed to convey a personality, above and beyond their utilitarian roots, starting life providing affordable transport to Europeans after WW 2, to the becoming the face of the flower power revolution of the 60's, they made films, books and songs about them.We travelled the world in the Beetle's big brother, the Kombi. I went from London to Africa and back in my second hand Dutch ex postal Kombi van.

If that is not success then I don't know what is.

Edit;I should confess my first car was a Blue 1966, 1600cc Beetle, my dad took me to the car yard and the car dealer said to dad, when talking about the reliability of the Beetle,"these things almost won the war you know".

 

[Art]

While not a bad rule of thumb...it really does depend on how it's going to be used and how much you want to customize a drive train.

So true... So True! I should have added to my post YRMV!

 

[sunchaser]

Porsche, Lamborgini, Ferrari?????

Ferarri and Lambos as well as Bugattis and Veyrons proudly proclaim "mid engine" as do the Toyota MR2 and Acura NSX if I'm not mistaken. Audi is even slipping mid engines into the fray

 

[psneeld]

Anyone that thinks adding a sterndrive to a boat has to balance it by adding weight foreward has NO CLUE about boat design.

Weight in a boat just has to be offset by buoyancy...no matter where you put that weight...if the hull shape has enough buoyancy to support it...it works...as long as the shape will conform to the original design requirements.

Some comments on this forum about boat design really scare me....

After getting all excited about I/Os I'm gonna bring up the bazillion designs that work just fine with engines in the cockpit with vee-drives...that ought to drive a few nuts around here....

The only thing worse than not knowing anything about boat design...is to try and compare boat design or marine engines with land counterparts...

 

[Bob Cofer]

Dang it!!!!

 

[hollywood8118]

Anyone that thinks adding a sterndrive to a boat has to balance it by adding weight foreward has NO CLUE about boat design.

Weight in a boat just has to be offset by buoyancy...no matter where you put that weight...if the hull shape has enough buoyancy to support it...it works...as long as the shape will conform to the original design requirements.

Some comments on this forum about boat design really scare me....

After getting all excited about I/Os I'm gonna bring up the bazillion designs that work just fine with engines in the cockpit with vee-drives...that ought to drive a few nuts around here....

The only thing worse than not knowing anything about boat design...is to try and compare boat design or marine engines with land counterparts...

Well said!

Engine foward = slow boat
Engine aft = fast boat ( in most cases )
A really fast boat needs as much of the weight on the transom ..to get the hull out of the water
Hollywood

 

[Art]

Well said!

Engine foward = slow boat
Engine aft = fast boat ( in most cases )
A really fast boat needs as much of the weight on the transom ..to get the hull out of the water
Hollywood

Dat Y me 1975 Johnson 50 hp O/B on da 1975 Crestliner Stinger tow behind runabout do 39.5 knots at WOT wit jus moi aboard!?!? Und, 20 + nmpg at 25 knots with me and da Admiral aboard!?!?

Dat Said:

Our 21K lb gross 34' Tolly TC with twin screws and 2 - 100 gal gas tanks in center of boat planes off real fast and smoothly. Handles well and with 510 total HP hits 21/22 knots at WOT with an easy 16 to 17 knot sustained cruising plane... for traveling purposes (at 1 nmpg).

 

[hollywood8118]

Dat Y me 1975 Johnson 50 hp O/B on da 1975 Crestliner Stinger tow behind runabout do 39.5 knots at WOT wit jus moi aboard!?!? Und, 20 + nmpg at 25 knots with me and da Admiral aboard!?!?

Dat Said:

Our 21K lb gross 34' Tolly TC with twin screws and 2 - 100 gal gas tanks in center of boat planes off real fast and smoothly. Handles well and with 510 total HP hits 21/22 knots at WOT with an easy 16 to 17 knot sustained cruising plane... for traveling purposes (at 1 nmpg).

Art,
22kts is not a "fast" boat.

My SeaRay had 700+ hp, planed @19kts@ 3000rpm@..80 nmpg
WFO...30KTS@4200RPM = 60GPH..OUCH!

I love my mid engined 270hp diesel ...2.5gph@1700@8kts.
Our dinghy now has a 40hp ob, its a avon 3.10 sport boat rib..
Will do 40 topped and cruise at about 10nmpg

"Mid engine" boats, no matter how much hp top out at about 50mph, all the power is being used to lift the hull vs. provide foward movement.
The exception to the rule is the hydroplane..think back to the old rolls royce and allison piston hydros
Hollywood

 

[Nomad Willy]

Well it looks like I've provided yo'all w some badly needed rant food.

Haha I even had a rear engined VW ...... in the 60s. Whatever car designs survive as the majority of all the designs should be considered best and the others are less desirable or ultimately failures. In the broad scope of things there is or/and was not very many rear engined cars. Better designs have evolved. Bias ply tires aren't popular anymore because Radial tires are better. Where's Marin when I need him.

"Engine foward = slow boat
Engine aft = fast boat ( in most cases )
A really fast boat needs as much of the weight on the transom ..to get the hull out of the water
Hollywood"

I'll except that Hollywood to a great extent. Small fast boats work better w weight aft and that is much of the reason most small boats have their engines aft. But there's much more to it. Before the IO there was OBs and IBs and before OBs there was just inboards. The engine evolution was predicated mostly on powerplant advantages and disadvantages ... not good balance. Balance was important to designers but the advantages of OB and IO power systems was even more important. As I've said before OBs work very well because of their lightness. And also because of several very obvious other reasons. IOs work well for obvious reasons as well but once off their trailer and underway the central engined IB is a better boat as far as balance, trim and the ability to pass over waves is concerned. But most often there is marketing concerns that override best balance like very valuable space in the center of the boat on small craft and the ease of operating in shallow water and being launched and retrieved from a trailer. For best balance the car engine would be located close to the center of the car too but is at one end to make room for the payload.

I hate to repeat myself BUT ..... As I said before I didn't say IOs won't work well I just said a centrally mounted IB engine provides the best balance. To me hull design and purebred configuration is most important. Fly bridges, galley up or down, excessive anchor rode weight or any other excessive weight, windage, carpet on the floor, TVs and all other things that distract from how well a boat will perform on the water is undesirable, questionable or totally unacceptable.

Huckin's and Canoe Cove made boats w engines (heavy DDs) in the stern and in the case of Huckin's there was considerable talk (here on TF) about their rough ride and I'm sure it wasn't all due to light construction. If the bow stays down a boats propensity to pound will be less ... considerably less and aft mounted engines promote light bows that are easily pushed high into the air by even small seas. And of course a bow in the air comes down hard on the dense sea under and causes unbearable discomfort for passengers or/and extreme forces on the hull .. or both. And also a boat out of the water lacks directional stability to some extent or worse and threatens acceptable control.

Again a rear engined car is poor design and a heavy engine far aft on a boat is not the ideal place for it from a boat balance and trim standpoint.
I think that's all I ever said.

 

[Insequent]

Grantm
I can understand you wanting more than 6 knots. But how much more - is 9 knots enough? If so then twin diesels, shaft drives are a good option. But hard to do in 30 ft boat - you need more waterline length to operate at that speed with good fuel efficiency. As much as you enjoy turning your own wrenches, if you have a stern drive you will soon be heartily sick of the maintenance effort and cost.

But if planing speed is what you want, then you need to minimize weight, so only one engine. But instead of the heavy truck/tractor models like JD, go for the marinized car types. Yanmar's 6BY260 is a good example. It only weighs 310 kg. It is based on the 3 litre BMW straight 6 they use in their cars, which has been ranked as the best car diesel engine around.

Will Allison ( Imaginocean Yacht Design ) designed a trailerable boat with one of these Yanmar's. The model is Graphite, 32 ft length, some photos & specs on the website. Claimed 32 knots.

Here is a youtube clip Graphite at 15 knots - Imaginocean Yacht Design - YouTube

and also an article Graphite - no carbon copy Boat News, Review & Advice - boatpoint.com.au

Its almost worth a visit to Hobart to look at it. He trailed it right up the East Coast a few years back. Being able to store in your yard is better than being in the water, but this is getting to be about the maximum easily achieved given our road registration rules.

 

[markpierce]

Gimme a low-RPM diesel engine with its propeller protected by a keel, any day.

 

[Codger2]

Again a rear engined car is poor design and a heavy engine far aft on a boat is not the ideal place for it from a boat balance and trim standpoint.
I think that's all I ever said.

I have to disagree with you, Eric. One of my favorite boats is the Mikelson 43 Zeus which has the engines all the way aft, directly below the cockpit. Huge teak hatches are powered open to access the ER. Once open, this allows you to stand up while performing checks or maintenance and makes it very easy to change an engine out. And since they're Cummins, Baker would love this feature. This boat has it all! A day head that is accessed from the cockpit, a salon & galley that all women love and 2 staterooms forward that will knock your socks off. The fly bridge is as elegant as the salon with two helm stations. One forward in the standard location and one aft, with full controls so that the skipper can have his cockpit and all fisherman in full view.

Mikelson 43 Sportfisher - Custom Fishing Boats for Sale

 

[Art]

Art,
22kts is not a "fast" boat.

My SeaRay had 700+ hp, planed @19kts@ 3000rpm@..80 nmpg
WFO...30KTS@4200RPM = 60GPH..OUCH!

I love my mid engined 270hp diesel ...2.5gph@1700@8kts.
Our dinghy now has a 40hp ob, its a avon 3.10 sport boat rib..
Will do 40 topped and cruise at about 10nmpg

"Mid engine" boats, no matter how much hp top out at about 50mph, all the power is being used to lift the hull vs. provide foward movement.
The exception to the rule is the hydroplane..think back to the old rolls royce and allison piston hydros
Hollywood

Yo, holly - I know dat! - LOL

But, don't let my my nearly 37 year ol' Tolly hear ya say dat, she might get tempermental when she flies past the D's and Semi D's... ha ha ha!!

I figure her WOT at 21/22 knots gets about or maybe even less than 1/2 nmpg (never kept her opened up long enough to calc fuel usage at that speed... and, don't intend to either!

I do know that running on either screw alone (other one shut down with its
BW trany in free wheel) that at 5.5 to 6 knots she gets 2.75 +/- nmpg. and with both engines runnining at 7 + knots she gets close to 2 nmpg. 7.58 knots is her mathmatical claced hull speed.

As I mentioned in previous post: Her 16/17 knot easy cruising speed on plane is right at 1 nmpg.

 

[Art]

I have to disagree with you, Eric. One of my favorite boats is the Mikelson 43 Zeus which has the engines all the way aft, directly below the cockpit. Huge teak hatches are powered open to access the ER. Once open, this allows you to stand up while performing checks or maintenance and makes it very easy to change an engine out. And since they're Cummins, Baker would love this feature. This boat has it all! A day head that is accessed from the cockpit, a salon & galley that all women love and 2 staterooms forward that will knock your socks off. The fly bridge is as elegant as the salon with two helm stations. One forward in the standard location and one aft, with full controls so that the skipper can have his cockpit and all fisherman in full view.

Mikelson 43 Sportfisher - Custom Fishing Boats for Sale

YUMMY - But, Can She Fly Too??? LOL

 

[Grantm]

Grantm
I can understand you wanting more than 6 knots. But how much more - is 9 knots enough? If so then twin diesels, shaft drives are a good option. But hard to do in 30 ft boat - you need more waterline length to operate at that speed with good fuel efficiency. As much as you enjoy turning your own wrenches, if you have a stern drive you will soon be heartily sick of the maintenance effort and cost.

But if planing speed is what you want, then you need to minimize weight, so only one engine. But instead of the heavy truck/tractor models like JD, go for the marinized car types. Yanmar's 6BY260 is a good example. It only weighs 310 kg. It is based on the 3 litre BMW straight 6 they use in their cars, which has been ranked as the best car diesel engine around.

Will Allison ( Imaginocean Yacht Design ) designed a trailerable boat with one of these Yanmar's. The model is Graphite, 32 ft length, some photos & specs on the website. Claimed 32 knots.

Here is a youtube clip Graphite at 15 knots - Imaginocean Yacht Design - YouTube

and also an article Graphite - no carbon copy Boat News, Review & Advice - boatpoint.com.au

Its almost worth a visit to Hobart to look at it. He trailed it right up the East Coast a few years back. Being able to store in your yard is better than being in the water, but this is getting to be about the maximum easily achieved given our road registration rules.

Thanks Insequent that makes sense. I'm only looking to do 12 knots at best. Be nice to cruise at 8 or 9 and push through a swell with some extra power if needs. I'm not after a speed boat that's for sure. Broken Bay in Sydney can be hairy place to navigate and I don't want to be at the mercy of this doing 6 knots.

I was looking at the 31 Mariners with twin 165 Pentas on shafts, I was just worried about the fuel cost of twins. Maybe it won't be too bad ?

All the advice is to steer clear of stern drives simply because of the cost to maintain and I have to admit I never had any trouble with my Perkins on a shaft it just needed more grunt.

I'm sure the right boat is out there I'm not in any hurry.

Many thanks guys !

 

[markpierce]

With a small, slow, 14-ton boat, don't feel any "push back" from waves. Spray? yes.

 

[FF]

The International engines come from TRUCKS , not lawn equipment , and they are still going strong.

They are currently used in operating as well as racing lobster boats with great sucess.

Rear engine work well in boats up on the plane as the surface area near the stern is carrying most of the weight on a fast boat.

A SD or barely plainning boat with most of the hull in the water at speed can have aft engines , but its more of a design challenge , tho with BMW and other car engines not too hard.


The BMW rides just fine , I ran a BMW R 60 US for over 100,000 miles with a fairing thru rain and snow year round (NYC)

The cylinders are just right shaking the bike from side to side instead of up into the riders crotch .
AS ankle warmers there nice in slush.


BMW got out of solo racing when tires got so good the cylinders would drag , so spent decades winning side car races with factory teams.

 

[psneeld]

I have to disagree with you, Eric. One of my favorite boats is the Mikelson 43 Zeus which has the engines all the way aft, directly below the cockpit. Huge teak hatches are powered open to access the ER. Once open, this allows you to stand up while performing checks or maintenance and makes it very easy to change an engine out. And since they're Cummins, Baker would love this feature. This boat has it all! A day head that is accessed from the cockpit, a salon & galley that all women love and 2 staterooms forward that will knock your socks off. The fly bridge is as elegant as the salon with two helm stations. One forward in the standard location and one aft, with full controls so that the skipper can have his cockpit and all fisherman in full view.

A well designed boat can have engines anywhere and it will work just fine...this midship requirement discussion and "need to balance" just shows a REALLY BASIC lack of knowledge about hull design.

The hundreds of thousands of successful boats out there is a reality...no matter what's someone's "preference is", it doens't make it true.

 

[SCOTTEDAVIS]

Well said!

Engine foward = slow boat
Engine aft = fast boat ( in most cases )
A really fast boat needs as much of the weight on the transom ..to get the hull out of the water
Hollywood

Like you said "most cases" sorry I had to.

 

[Art]

Current plane worthy hard chine 1977 Tollycraft TC has twin straight drives as well as 2 100 gal fuel tanks amidship and to hull sides w/ 77 gal water (in two tanks to either side) up against transom. 1973 plane worthy 31' Uni had twins to rear using V-drive and 150 gal fuel tank centerline amidship with 50 gal water tank forward and centerline.

Both designs work very well. The Reason: Both manufacturers were very conscious as to the importance of hull design in accordance with weight distribution and interior layout. Soooo... both these boats were well founded via intense marine engineering by some of the best boat and hull designers in the industry.

I am confident that there is capability to arrange weight distribution (engines included) as compared to hull design in myriad of ways and still have very efficient boats. It’s all in the engineering!

 

[hollywood8118]

Like you said "most cases" sorry I had to.

missed the part where I mentioned hydro's did you?

HOLLYWOOD

 

[Nomad Willy]

Walt you make my previous point very well. Balance is not top priority for most people. Of all the things you raved about in the Mikelson boat balance wasn't one of them.

And Art yes the Uniflite was designed such that it would carry a lot of weight aft unlike the Tolly. The Uniflite had a "warped" bottom kinda like a Mainship 34. All the way back to the transom those boats were still becoming flatter right up to the transom. An easy way to spot a warped bottom is to observe that the chines drop all the way aft to the transom whereas on most boats the chine is basically horizontal from amidships aft. The extreme warped boat could have a sharp and deep forefoot leading to a moderately deep V amidships leading to a bottom at the transom straight across w no deadrise (V) or even reverse deadrise like the Hickman sea sled. So the aft part of the boat is better equipped to carry weight than a constant deadrise boat such as a Tolly. Also the Tollycraft boats had a considerably narrower chine and it was (as I recall) the same aft as amidship. Constant deadrise amidships to the transom. Under certain circumstances the warped bottom can create lift w/o any angle of attack at all whereas the constant deadrise hull needs angle of attack. And Hollywood I'm not talk'in really fast boats. This is indeed a trawler boat forum.

SCOTTEDAVIS yes the hydroplane is more dependent on balance than the Yacht. Marketing stuff need not apply. And still the hydro's tend to flip now and then.

FF wrote "The BMW rides just fine , I ran a BMW R 60 US for over 100,000 miles with a fairing thru rain and snow year round (NYC)". Yup but a slight crouch was needed to place one's feed far enough aft to clear the cyl heads/carbs. The "K" bikes were even worse. I had a R100 and a K75. And the boxer twin low speed shake was terrible. Why do you suppose almost no other motorcycle manufacturer made boxer bikes? Not a very good design. And I'm not going to touch the dragging cylinder issue.

Grantm, Good luck. That's what I'd like too .. a good 12 knot boat. Almost nonexistent though.

 

[Art]

Art yes the Uniflite was designed such that it would carry a lot of weight aft unlike the Tolly. The Uniflite had a "warped" bottom kinda like a Mainship 34. All the way back to the transom those boats were still becoming flatter right up to the transom. An easy way to spot a warped bottom is to observe that the chines drop all the way aft to the transom whereas on most boats the chine is basically horizontal from amidships aft. The extreme warped boat could have a sharp and deep forefoot leading to a moderately deep V amidships leading to a bottom at the transom straight across w no deadrise (V) or even reverse deadrise like the Hickman sea sled. So the aft part of the boat is better equipped to carry weight than a constant deadrise boat such as a Tolly. Also the Tollycraft boats had a considerably narrower chine and it was (as I recall) the same aft as amidship. Constant deadrise amidships to the transom. Under certain circumstances the warped bottom can create lift w/o any angle of attack at all whereas the constant deadrise hull needs angle of attack.

Eric - Adjustable trim tabs work wonders too! On both types of hull/bottom designs

 

[Nomad Willy]

The need for trim tabs is probably really a need to have a better balanced boat .... lots of small boats being an exception due to variable load distribution. A boat w an engine amidships and good balance shouldn't require tabs. Tabs are probably mostly employed on IO boats. And I think their lift to drag ratio is questionable at best. But a badly out of balance boat can probably be rendered more efficient w tabs but I'm guessing moving weight fwd and removing the tabs would probably produce a more efficient boat yet.

One exception to the above could/would be a fast trawler w very large fuel tanks in the laz. Lift in the stern would be needed especially if it planed but I wouldn't consider that good design if the tabs were actually needed. Fuel tanks fwd is the answer so CG is maintained over time. Balanced boat.

 

[Art]

The need for trim tabs is probably really a need to have a better balanced boat .... lots of small boats being an exception due to variable load distribution. A boat w an engine amidships and good balance shouldn't require tabs. Tabs are probably mostly employed on IO boats. And I think their lift to drag ratio is questionable at best. But a badly out of balance boat can probably be rendered more efficient w tabs but I'm guessing moving weight fwd and removing the tabs would probably produce a more efficient boat yet.

One exception to the above could/would be a fast trawler w very large fuel tanks in the laz. Lift in the stern would be needed especially if it planed but I wouldn't consider that good design if the tabs were actually needed. Fuel tanks fwd is the answer so CG is maintained over time. Balanced boat.

Eric

There can be no such thing as a perfectly balanced boat 100% of the time. As fuel is used substantially sized weight areas alter. Same with water usage. Same with provisions and cloths storage areas and usage. As well as added appendages such a dink/motor... and... even crew/passengers while they move into different locations aboard. A marine engineer’s effort to have a particular boat/hull design “perfectly balanced” is calculated by using optimum weight distributions and is averaged over the scope of the boat... but, to have a boat always remain perfectly balanced is actually just a dream. Therefore trim tabs are a wise investment that can create better boat travel... especially for planing hulls, trawlers included.

Two or three 200 lb people on port then starboard will definably alter most 30’ to 45’ boat's vertical attitude. Or if they move forward to aft its horizontal level will change. All in all trim tabs that work both independently or individually do a really good job of counteracting weight distribution changes as a boat moves through water. Especially on a planing hull when it is cruising at well beyond hull speed. Speaking of planing hull, while on plane... and depending on the speed of plane, therein the differencing horizontal level a boat encounters at various speeds, trim tabs can adjust boat’s horizontal level to develop more comfort and/or better nmpg.

 

[psneeld]

Shamrock Keel Drive boats were a semi-displacement (near New England style lobster boat hull ) with engine amidships....they DEFINITELY need tabs unless you get the commercial pilothouse forward or run them at the pin all the time to keep the bow down far enough to see over..

Tabs are also standard on about every sportfishing inboard boat I know of to help with planning off, changing loads and side to side trim when running.

 

[AusCan]

Grantm -
If you are open to a smaller boat, this little beauty really catches my eye.
Arvor Weekender 700 by Arvor Boats Australia

They really pack a lot into a small boat.

It has a single Cummins 150hp diesel shaft drive, does 22 knots, and they are trailerable. They are quite popular with fisherman in SA and seem to handle rough water very well.

They've only been around for a few years, but a few used ones are starting to come on the market. If I was after a newer boat, I'd certainly consider one.

 

[CPseudonym]

Grantm - If you are open to a smaller boat, this little beauty really catches my eye. Arvor Weekender 700 by Arvor Boats Australia They really pack a lot into a small boat. It has a single Cummins 150hp diesel shaft drive, does 22 knots, and they are trailerable. They are quite popular with fisherman in SA and seem to handle rough water very well. They've only been around for a few years, but a few used ones are starting to come on the market. If I was after a newer boat, I'd certainly consider one.

There's a lot to like in that boat. Easy to see why it catches your eye. Good looking boat.