boat stable in water

[paulga]

I went on deck of a 34' Mainship motor yacht.
Boat is spacious inside, living to the name of a "floating condo".
But it was constantly wiggling side to side, with the wind. At times, I almost lost a steady foothold. If I liveaboard, I would be also rolling constantly.

Does all boats of similar size roll like this in water with wind? are there some boats that are more stable?

 

[BruceK]

No they don`t. To my observation, the more the hull is designed towards planing, the more it "hunts" when lying into the wind on anchor or mooring. It`s "sitting on" the water rather than "sitting in" the water. Very noticeable in a breezy mooring field, especially on a less susceptible boat, and it can`t be pleasant for the crew.

 

[paulga]

No they don`t. To my observation, the more the hull is designed towards planing, the more it "hunts" when lying into the wind on anchor or mooring. It`s "sitting on" the water rather than "sitting in" the water. Very noticeable in a breezy mooring field, especially on a less susceptible boat, and it can`t be pleasant for the crew.

Thanks for the quick reply.
so a motor yacht is made for planing the water.
are you saying the boats with a deeper draft will be more stable, because it sit in the water more?
could you show some examples of more stable boat styles?

 

[Comodave]

Which Mainship 34’? It makes a difference.

 

[BruceK]

Many boat for sale adverts on the various sites include an out of the water hull picture, for various reasons. If you search some boats you have in mind, you`ll see differences between say, a Mainship (though apparently they vary within the brand) and say, a Grand Banks 36 or 42.
Many of our trawler style boats are said to be "semi displacement"(?= semi planing) hulls rather than "planing". IMO hulls can fall anywhere in between the two. A "full displacement" hull is smooth (no chines). Try a search on hull design looking for planing, semi and full displacement hulls, you`ll soon see the difference. Each has its own pluses and minuses. And other TFers with may more expertise are sure to chime in here.

 

[magna 6882]

Your observations are what we saw in some boats when we were shopping. Some boats, when stepping aboard at dock would list immediately .We didnt even test these on the water. Our current boat barley moves when stepping aboard and i dont notice any boat movement when passengers are walking around. I am not sure if its hull depth or as stated a planning hull design thing.

 

[ranger58sb]

I went on deck of a 34' Mainship motor yacht.
Boat is spacious inside, living to the name of a "floating condo".
But it was constantly wiggling side to side, with the wind. At times, I almost lost a steady foothold. If I liveaboard, I would be also rolling constantly.

Does all boats of similar size roll like this in water with wind? are there some boats that are more stable?

Which 34? The only Mainship I remember that might have been called a "motor yacht" would have been in the early to mid '90s models... not their earlier and later "trawler-sorta" boats.

The early 34s were only a 12' beam, so yes, could get rolly in a boisterous anchorage or slip. (I'd not have thought of those as spacious or "floating condo" either.) I'd guess the later, wider-beam, models might have been less tippy.

-Chris

 

[ranger58sb]

Your observations are what we saw in some boats when we were shopping. Some boats, when stepping aboard at dock would list immediately .We didnt even test these on the water. Our current boat barley moves when stepping aboard and i dont notice any boat movement when passengers are walking around. I am not sure if its hull depth or as stated a planning hull design thing.

It's probably partly, at least, displacement. Your 45 likely outweighs any Mainship 34 by a factor of 2x, 3x, or maybe even morex

-Chris

 

[rslifkin]

Your observations are what we saw in some boats when we were shopping. Some boats, when stepping aboard at dock would list immediately .We didnt even test these on the water. Our current boat barley moves when stepping aboard and i dont notice any boat movement when passengers are walking around. I am not sure if its hull depth or as stated a planning hull design thing.

Hull shape, total weight, and weight distribution within the hull all have a significant effect on how tender the boat feels (in terms of low angle roll such as stepping on and off).

My boat feels noticeably tender when getting on from a dock (14' beam, 38' hull length, ~27k lbs). But I've been on similar size boats that weighed less, were a faster planing hull with less draft, but felt more solid when stepping on and off. One was of similar overall beam, but had less flare to the hull, so slightly wider waterline beam. Another was narrower than my boat. The big difference? My tanks are all along the centerline, the fuel tanks were outboard saddle tanks on both other boats. More weight out towards the sides makes it harder to start a small roll, so the boat typically feels less tender.

 

[paulga]

Which 34? The only Mainship I remember that might have been called a "motor yacht" would have been in the early to mid '90s models... not their earlier and later "trawler-sorta" boats.

The early 34s were only a 12' beam, so yes, could get rolly in a boisterous anchorage or slip. (I'd not have thought of those as spacious or "floating condo" either.) I'd guess the later, wider-beam, models might have been less tippy.

-Chris

it's a motor yacht built by Mainship in '96. Hull shape is Modified Vee, Beam 13.5', depth 6.9'. dry weight is 8.4T

 

[paulga]

Hull shape, total weight, and weight distribution within the hull all have a significant effect on how tender the boat feels (in terms of low angle roll such as stepping on and off).

My boat feels noticeably tender when getting on from a dock (14' beam, 38' hull length, ~27k lbs). But I've been on similar size boats that weighed less, were a faster planing hull with less draft, but felt more solid when stepping on and off. One was of similar overall beam, but had less flare to the hull, so slightly wider waterline beam. Another was narrower than my boat. The big difference? My tanks are all along the centerline, the fuel tanks were outboard saddle tanks on both other boats. More weight out towards the sides makes it harder to start a small roll, so the boat typically feels less tender.

this makes sense. a wider bottom make it more squre. but the waterline beam on the 34' motor yacht was not narrow, i cannot tell the difference comparing with another boat's waterline beam. and all motor yachts / trawlers that I have seen have fuel tanks inside hull, not outboard?

 

[paulga]

Your observations are what we saw in some boats when we were shopping. Some boats, when stepping aboard at dock would list immediately .We didnt even test these on the water. Our current boat barley moves when stepping aboard and i dont notice any boat movement when passengers are walking around. I am not sure if its hull depth or as stated a planning hull design thing.

it was more by the wind. when I walk off the boat, I noticed it was rolling with the wind

 

[rslifkin]

this makes sense. a wider bottom make it more squre. but the waterline beam on the 34' motor yacht was not narrow, i cannot tell the difference comparing with another boat's waterline beam. and all motor yachts / trawlers that I have seen have fuel tanks inside hull, not outboard?

By "outboard", I meant out at the sides, but still inside the hull. On my boat, all of the tanks are pushed as far to the centerline as they can be. But on some, the tanks are as far out to the sides as possible (such as on either side of the engine(s). That weight distribution has a noticeable impact on roll behavior.

 

[mvweebles]

What type of weather and how was the boat tied? I'm currently in a floating dock slip with no finger on one side - shared space with the adjacent boat so no way to secure one of the four corners. Boat definitely moves a bit more, and can be a bit abrupt as it hits the end of a dockline tether. It was pretty stormy a couple days ago with gusts in the 35-40 kt range and there was definitely a fair amount of motion. Finally, I've been at marinas where there was a fair amount of surge or wake traffic - boat dances quite a bit there.

Not saying boat design and characteristics don't play a role - high windage and/or lightweight boats are of course influenced by wind. Boat with a lot of keel in the water like nine will feel currents. Round bottom boats like mine will be more tender, at least initially. But weather and conditions are very high on the influencer list.

Peter

 

[mvweebles]

Your observations are what we saw in some boats when we were shopping. Some boats, when stepping aboard at dock would list immediately .We didnt even test these on the water. Our current boat barley moves when stepping aboard and i dont notice any boat movement when passengers are walking around. I am not sure if its hull depth or as stated a planning hull design thing.

What you are describing is often called "tenderness." As mentioned in the previous post, displacement boats often have a fair amount of initial tenderness until the ballast kicks in. Initial stability is low, ultimate stability is high. So there may not be a good correlation between initial stability and underway stability.

Wide boats - those with low length to beam ratios (3:1 is average, boats like Tiara, Regal, and even some Bayliners can approach 2.5:1; or catamarans that approach 2:1)) are pretty stiff, at least initially.

Peter

 

[paulga]

By "outboard", I meant out at the sides, but still inside the hull. On my boat, all of the tanks are pushed as far to the centerline as they can be. But on some, the tanks are as far out to the sides as possible (such as on either side of the engine(s). That weight distribution has a noticeable impact on roll behavior.

it looks like the fuel tank are on side of engines

 

[sunchaser]

In that size range, whether a SeaRay, Nordic Tug, Carver, Bayliner, Mainship or Tollycraft the boats are designed light with little excess weight down low which is important for stability. The above waterline shapes greatly influence sailing at anchor with these intentionally light hulls.

So yes size and weight matter. BTW those 454s are not fuel miserly but that's what is needed to get that vessel on a plane. I've found that sport fishing and down east styles in this size range are more dock and at anchor stable due to weight being lower.

 

[PM]

All those responses and nobody mentions keel. Full and semi displacement hulls generally have a full keel. That is from front to stern, including an enclosure of sorts for the prop, generally securing the bottom of the rudder.

Picture a slab of wood (or whatever) about 36 - 45 feet in length starting at a few inches in depth and ending up at around two feet in depth at the stern. Maybe an average of a foot or more. Now picture this slab suspended horizontally in the water, at a depth of three feet. Now try to drag this slab sideways through the water. It would take a LOT of energy.

Take a look at any boat you are considering purchasing (not sailboats) and consider the keel and what it is doing for the stability of the boat.

pete

 

[CharlieO.]

There is a similar boat in our marina. There is way more boat out of the water than in the water and tons of canvas topside.

 

[paulga]

Many boat for sale adverts on the various sites include an out of the water hull picture, for various reasons. If you search some boats you have in mind, you`ll see differences between say, a Mainship (though apparently they vary within the brand) and say, a Grand Banks 36 or 42.
Many of our trawler style boats are said to be "semi displacement"(?= semi planing) hulls rather than "planing". IMO hulls can fall anywhere in between the two. A "full displacement" hull is smooth (no chines). Try a search on hull design looking for planing, semi and full displacement hulls, you`ll soon see the difference. Each has its own pluses and minuses. And other TFers with may more expertise are sure to chime in here.

Thanks. I kind of get the idea of the factors that impact stability.
would a trawler like PT 35 sundeck more stable than the Mainship 34 motor yacht?

 

[CharlieO.]

Thanks. I kind of get the idea of the factors that impact stability.
would a trawler like PT 35 sundeck more stable than the Mainship 34 motor yacht?

I'm betting the PT 35 is at least twice the weight of the Mainship MY.

 

[paulga]

I'm betting the PT 35 is at least twice the weight of the Mainship MY.

no, it's only 500 lbs more. should be from the larger diesel engines.
diesel engines have much higher maintenance costs, that's why i didn't actively look into those.

 

[Delta Riverat]

My Gypsy is pretty stable. I notice boats next to me rocking more then me. On boarding when you step on the gunwale, hardly any movement.

But then it weighs 21 tons and has a 15 foot beam and draws 4.5 feet.

 

[paulga]

Thanks. I learned V hull is designed for planing, semi hull does not roll as much. so I will look for semi hull.

 

[CharlieO.]

no, it's only 500 lbs more. should be from the larger diesel engines.
diesel engines have much higher maintenance costs, that's why i didn't actively look into those.

Thats surprising to me, that must be the performance in PT - lighter weight to go faster maybe?

 

[ranger58sb]

it's a motor yacht built by Mainship in '96. Hull shape is Modified Vee, Beam 13.5', depth 6.9'. dry weight is 8.4T

Ah. From Mainship's "in between" (non-trawler) years. Lightweight, top-heavy boat with a planing hull.

diesel engines have much higher maintenance costs, that's why i didn't actively look into those.

That might depend on what you mean by "much" and it could also be mostly a non-issue if you're intending to do most of the maintenance yourself. And it could also depend on which diesels; some of the most basic don't need much.

And then finally, some depends on your intended usage. Dock queen and gas engines go together fairly well. A few/short trips, still gas. Once you start getting into high mileage and/or high hours/year, diesels can end up being less expensive in the long run.

There's probably a thread (or 200) on it, but if you can't find something useful, you could start a separate thread about the cost of diesel maintenance. Depends on the specific engine, in a specific use case... but some may say it's an "annual" oil and filter change, fuel filter change, impeller change... plus occasional coolant/filter changes... and an occasional heat exchanger flush. Not much more than that on some of the more basic diesels...

-Chris

 

[KnotYet]

...
diesel engines have much higher maintenance costs, that's why i didn't actively look into those.

About the only higher cost for a diesel would be more quarts of oil at each change.
You probably would save that by not needing spark plugs and wires, etc.

I suppose if you were looking at diesels with aftercoolers that does add some cost.
Comparable HP gas engines would use lots more fuel so even that might average out.

 

[paulga]

Ah. From Mainship's "in between" (non-trawler) years. Lightweight, top-heavy boat with a planing hull.




That might depend on what you mean by "much" and it could also be mostly a non-issue if you're intending to do most of the maintenance yourself. And it could also depend on which diesels; some of the most basic don't need much.

And then finally, some depends on your intended usage. Dock queen and gas engines go together fairly well. A few/short trips, still gas. Once you start getting into high mileage and/or high hours/year, diesels can end up being less expensive in the long run.

There's probably a thread (or 200) on it, but if you can't find something useful, you could start a separate thread about the cost of diesel maintenance. Depends on the specific engine, in a specific use case... but some may say it's an "annual" oil and filter change, fuel filter change, impeller change... plus occasional coolant/filter changes... and an occasional heat exchanger flush. Not much more than that on some of the more basic diesels...

-Chris

valve lashing, fuel filtration, cooling system etc. are included in 1k hour maintenance. Are these be easy D-I-Y work?

i heard mixed opinions. From some threads the cost is high. see post #19 of https://www.thehulltruth.com/boating-forum/1127544-diesel-engine-maintenance.html

there are other posts saying $20k service quote for each side.

 

[sunchaser]

For maintenance in addition to going by the book pull up a relevant utube video for these marine engines. They are PFI with electronic ignition which is a plus. Likely change the exhaust risers. Oil, filters, plugs and wires. Valve adjustment etc.

As the boat sits you should smell no gasoline before starting or after shutdown. A good mercruiser survey guy will know what to look for. Good luck and keep us posted.

 

[KnotYet]

valve lashing, fuel filtration, cooling system etc. are included in 1k hour maintenance. Are these be easy D-I-Y work?

i heard mixed opinions. From some threads the cost is high. see post #19 of https://www.thehulltruth.com/boating-forum/1127544-diesel-engine-maintenance.html

there are other posts saying $20k service quote for each side.

You seem to cherry pick the posts on THT to reference. I didn't see many that
claimed diesels cost much more to maintain than those Crusaders, for example.
TCO for diesels will almost always be less than for gas engines, as well. A lot
depends on how much you use the boat. The more use, the better diesel looks.