Plumb Bows, Slab Sides, and Wet Decks

[OceanSeaSpray]

Originally Posted by wingssail

...
What happens is this: The bow slices off a piece of the wave, throws it up in the air, where the wind blows it back onto the deck. It can be quite a bit of water, at times. Even my boat, which does not have a plumb bow, can land six inches of water on the foredeck, which is then rushing back towards us. We duck for cover behind the dodger, and hopefully stay dry. The helmsmen, if we are not on the vane, gets wet.
...

Some do exactly that indeed, but it is no rule and they certainly do less so with a steeper stem and good freeboard, because the "knife" tends to be sharper and it cuts without parting the water as violently. I hardly throw any spray up to weather upwind.

The wettest angle for me is a beam reach in a fresh breeze and short sea, because the odd crest can slap the windward hull and throw spray up in the air. With 9-10 knots of boat speed, this can land right in the cockpit by the time it comes down. It only happens now and then, but it can be wet.
Slower would seem drier because it wouldn't fall as far back, but nothing to do with the bow.


Now this reminds me of people who were ocean cruising on a J/160 some years ago. The owner was quite an experienced and capable sailor. We had met in Durban, so they had just crossed the Indian Ocean. That boat was shipping enough solid water over the deck from the bow, they could get hit so hard at the helm that they needed to be solidly harnessed and this didn't entirely exclude injuries.



Upwind, it pounded, and on a run, it would quite readily bury the bow in, and this was still more or less tropical cruising. For a 53' hull, it has an unusually narrow beam (4.42m or 14.5'), it is very fine and low forward. I went back to my notes and the freeboard at the stem was only 1.3m. At speed in a lumpy sea offshore, it could literally penetrate the wave instead of lifting, and it would then wash over all the way back.

Sometimes, bad designs (from a given point of view at least) are even more interesting than good ones because they show us where limits are. It usually doesn't come down to a single feature, there are combinations that work and others that don't, like fast skinny boats with little freeboard and little volume forward. Successful modern hulls tend to offer a good beam amongst other things.

[DeepFrz]

wingsail, I don't have a point. I am just asking questions, commenting on observations. Someone posts links to two videos and in one I see a nice gentle more traditional boat with good manners and in the other a plumb bow slab sided boat bouncing around, hobby horsing and slamming into the seas. WTF is that. They certainly weren't doing 30 knots when they had to change points of sail to keep the camera dry. The crew's comment, not mine. Then someone says keep the weight out of the ends and someone posted a video of a beautiful boat flying through the sea with all the moveable ballast (crew) jammed into the stern. Do you keep the weight out of the ends or not. I'm just askin is all???

[DeepFrz]

Commenting on the last post it all comes down to design. Speaking from a cruising perspective I loved the video of the Rustler. From a racing perspective I love watching the Open 60's.

Edit: until the Open 60's lose their keels, that is...

[DeepFrz]

One more comment on design. I think one of the most appropriate cruising boats to come off the boards in a long time is the Garcia Exploration 45.

[daddle]

Originally Posted by DeepFrz

... Do you keep the weight out of the ends or not. I'm just askin is all???

DeepFrz already know the answer, but for others: Yes. Keep the weight out of the ends. It makes a significant difference in pitching and splashing. Boats like in the picture above have fat sections aft which when at speed can support the crew being aft. Especially with all that sail power pushing the bow down.

I move the anchor and chain back to near the mast step before any offshore sail. Nothing is ahead of the foredeck hatch except the v-berth mattress and windlass (grrrr). Seriously, nothing. Even the bow roller comes back. The result is an astonishing lack of pitching which one needs to experience to believe. Fairly plumb bow, very narrow, slab sides. The ride is superb. Very much worth the 30 minutes work moving everything.

Nothing but fenders in the aft locker, either.

The way water gets over the boat is the occasional wave that smacks the bow, as said above, and gets lofted back the deck by the wind. There's no submarine-ing. There's no big curling bow wave. There's no bow pitching skyward. And the speed stays up. No stalling on waves. The tradeoff is some pounding at times. But, hey, catamaran people put up with much more pounding and slamming so how bad can it be? I prefer some annoying pounding to slow wallowing, yawing and pitching like a pig in mud.

[Polux]

Originally Posted by DeepFrz

One more comment on design. I think one of the most appropriate cruising boats to come off the boards in a long time is the Garcia Exploration 45.

We are talking about hulls. In what regards hulls the Garcia 45 is a very typical modern hull, the same of the Allures 45. What separates the boat from mass production boats is not the hull design but the particular interior more suited to cold climates and some interior reinforcements due to the particular use of the boat.

[Polux]

Originally Posted by OceanSeaSpray

Some do exactly that indeed, but it is no rule and they certainly do less so with a steeper stem and good freeboard, because the "knife" tends to be sharper and it cuts without parting the water as violently. I hardly throw any spray up to weather upwind.

The wettest angle for me is a beam reach in a fresh breeze and short sea, because the odd crest can slap the windward hull and throw spray up in the air. With 9-10 knots of boat speed, this can land right in the cockpit by the time it comes down. It only happens now and then, but it can be wet.
Slower would seem drier because it wouldn't fall as far back, but nothing to do with the bow.


Now this reminds me of people who were ocean cruising on a J/160 some years ago. The owner was quite an experienced and capable sailor. We had met in Durban, so they had just crossed the Indian Ocean. That boat was shipping enough solid water over the deck from the bow, they could get hit so hard at the helm that they needed to be solidly harnessed and this didn't entirely exclude injuries.



Upwind, it pounded, and on a run, it would quite readily bury the bow in, and this was still more or less tropical cruising. For a 53' hull, it has an unusually narrow beam (4.42m or 14.5'), it is very fine and low forward. I went back to my notes and the freeboard at the stem was only 1.3m. At speed in a lumpy sea offshore, it could literally penetrate the wave instead of lifting, and it would then wash over all the way back.

Sometimes, bad designs (from a given point of view at least) are even more interesting than good ones because they show us where limits are. It usually doesn't come down to a single feature, there are combinations that work and others that don't, like fast skinny boats with little freeboard and little volume forward. Successful modern hulls tend to offer a good beam amongst other things.

New fast cruising designs start to use chines at the bow with a double function: Increase lift and deflect the water to the sides.

[DeepFrz]

Aventura IV (Garcia Exploration 45), plumb bow, slab sides, wide flat aft sections. Lifting keel. Double rudders. Chain locker and windlass mid ships. Watertight bulkheads fore and aft. Beachable. Built in outside protection for the on watch crew plus the crew can stand much of the watch inside. Many design decisions to produce what is proving out to be a great cruising design.

The first 10,000(?) miles, many of them waters with ice have been very successful. I believe that three have been delivered.

[OceanSeaSpray]

Originally Posted by Polux

New fast cruising designs start to use chines at the bow with a double function: Increase lift and deflect the water to the sides.

Hmm yes, I think you can go too far either way. The bow still needs to cut through, otherwise pitching or just plain stalling in a short steep sea is what happens next.

Running the chine all the way into the stem might not be much of a winner, but rather a modern-looking take on the old fat and blunt forward once the water is no longer flat. Power boats punch upright, but sailing yachts don't. They certainly don't need a chine forward to be dry.

There is a lot of funny-looking stuff being drafted all around, but good sea boats are far and few in-between. Many of them dip the nose down as they heel, something quite hard to prevent when the waterline beam is carried aft, and those boats are not worth having.

Eric

[wingssail]

OceanSeaSpray, I have just spent an hour reading your web site Nordkyn Design - Yacht Design and Engineering, so I know you know what you're talking about, (and BTW I agree with your points there and was happy to find someone who could make them so eloquently, especially regarding weight aloft and in the ends) but lets have a little tolerance here for what some of the designers are trying to achieve in the newer designs.

"not worth having"? That is a bit harsh.

For example I just sailed this weekend, in the open ocean, on a racing boat with a plumb bow, slab sides, and absolutely the widest point of the yacht was the transom. It sailed fine. It did not sail bow down, as intuitively we would think it must. It was dry, (there weren't big waves) and handled well on every point of sail.

No, it did not have chines, however, I'd guess that the chines we see on some cruising designs are modeled after some high end racing yachts which are looking for a little more buoyancy on that high speed run, not to keep dry when beating. On the cruising designs, maybe it is more marketing than anything else. OK, I don't care about that, I don't think it hurts them. Anyhow, a lot, the vast majority, of cruising yachts do stand totally upright when pounding to weather, because they are motoring. Maybe in that case the extra flare below the chine does help them keep dry.

Fred

[OceanSeaSpray]

Originally Posted by wingssail

OceanSeaSpray, I have just spent an hour reading your web site Nordkyn Design - Yacht Design and Engineering, so I know you know what you're talking about, (and BTW I agree with your points there and was happy to find someone who could make them so eloquently, especially regarding weight aloft and in the ends) but lets have a little tolerance here for what some of the designers are trying to achieve in the newer designs.

"not worth having"? That is a bit harsh.

For example I just sailed this weekend, in the open ocean, on a racing boat with a plumb bow, slab sides, and absolutely the widest point of the yacht was the transom. It sailed fine. It did not sail bow down, as intuitively we would think it must. It was dry, (there weren't big waves) and handled well on every point of sail.

No, it did not have chines, however, I'd guess that the chines we see on some cruising designs are modeled after some high end racing yachts which are looking for a little more buoyancy on that high speed run, not to keep dry when beating. On the cruising designs, maybe it is more marketing than anything else. OK, I don't care about that, I don't think it hurts them. Anyhow, a lot, the vast majority, of cruising yachts do stand totally upright when pounding to weather, because they are motoring. Maybe in that case the extra flare below the chine does help them keep dry.

Fred

Fred,

Maybe I should have worded more cautiously! I was referring to the bow-down attitude, not the shape or look of the hull when I said "not worth having". It is very possible to design hulls that don't exhibit that heel-trim coupling and still have plenty of beam aft, it is just that you really need to work to get it.
When they do trim down by the nose, every time they roll in a seaway, resistance also moves forward and that is a great recipe for course instability and handling problems.

Also, if you look carefully, many "triangular" hulls at the deck, maximum beam at the transom (like Open 60s etc), are not triangular at all at the waterline. They tuck back in, they have highly engineered shapes.
Maximum beam transoms on cruising boats are a bit of an open question. That is a lot more boat weight right at the stern for a start. Then it allows for arrangements like twin wheels etc.

I think the chines aft started with the Class 40 Akilaria some time ago and there was some sense behind the idea. Next thing we started seeing Beneteau cruisers with a chine aft where it can't possibly do anything, but they just had to have it.

Eric

[Polux]

Originally Posted by OceanSeaSpray

Hmm yes, I think you can go too far either way. The bow still needs to cut through, otherwise pitching or just plain stalling in a short steep sea is what happens next.

Running the chine all the way into the stem might not be much of a winner, but rather a modern-looking take on the old fat and blunt forward once the water is no longer flat. ....
Eric

No, that chine design comes from racing boats. When going downwind it adds buoyancy and takes spray away and when going upwind you are looking it on the wrong position because if downwind the boat goes almost upright, upwind goes heeled with the chine at the bow (and transom) on the water increasing stability and power.

Here, on the new Pogo 40class racer you have the same basic chine design:

https://www.youtube.com/watch?v=osFEjGyXMZI

[goboatingnow]

most overhangs got designed in historically as racing rule beaters. these days the rules are different and more hydrodynamic designs are gaining strength.

[Terra Nova]

Originally Posted by OceanSeaSpray

...Maximum beam transoms on cruising boats are a bit of an open question. That is a lot more boat weight right at the stern for a start. Then it allows for arrangements like twin wheels etc...

I think you have that reversed. And you mention twin wheels like they are actually desirable. Twin wheels are the compromise you must accept if you insist on carrying such great beam so far aft. Otherwise 1 large wheel would suffice.

[Polux]

Originally Posted by goboatingnow

most overhangs got designed in historically as racing rule beaters. these days the rules are different and more hydrodynamic designs are gaining strength.

Specially when there are very few rules like on the Open boats and class40 without being Open boat gives a great liberty to designers: They are not boats with a rating but boats with a free design inside a fixed set of rules. Chines of any type will not interfere with the rules, but regarding the bow they had to limit creativity and type of bows otherwise all new ones would come with big rounded bows, making older boats obsolete.