What makes a boat "wet / dry" at sea

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paul salliss

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It would appear that boats described as "wet" such as an Aquastar for example are often semi displacement boats and yet this category of "wet" boats are renowned for great sea keeping. Is the boat wet because the boat is actually punching through the waves which deposits some of this water back over the bow. I am interested in owners thoughts on this and if this "wet" boat scenario has in any way put them of semi d style boats
 
That's my understanding exactly.

A dry boat will simply float on top of the waves feeling every bump and suffering a lot of slamming. This can be reduced by hull shape and by more weight but this makes a boat slower and these boats fall into the semi-displacement category.

The ultimate wet boat would be a submarine and these give can give a very smooth ride!
 
i have a nelson 34, meant to be a `wet` boat i am told! great head through the waves but rolls badly with anything side on.
 
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Wet Boat, Dry Boat

I would say as a generalisation that semidisplacment are prone to be wetter than planing hulls due to the fact that a lot of semidisplacemnt hulls give a soft landing by not decellerating fast when thy hit the wave but having a fine entry and progressively burrying their bow in the wave.

Planing boats tend to have a wide full bow and spray rails to stop the bow burrying , this can give a hard landing.

The semidisplacemnt boats I have had 2 of Mitchel 31, a Halmatic 34 and an Aquastar 48 all tend to be a bit wet certainly the last two are the SD boats I have cruised extensively with and push the weather limits from time to time. They tended when you hit a wave to throw it up in the air and it either blows over you from the left or the right. I had a fairline 36 sedan, planing boat setween the last two sd's as a useful comparator.

Certainly bow shape will improve the dryness so a wide bow above the waterline with flare of bow turning the water away and not up will help.

Spray rails or steps above the waterline at the bow will turn the water away and down when you hit a wave.

So If I was about to design a hull for the ultimate Semidisplacemnt dry ride.

Fine entry to waterline, with spray rails below WL.

Above the waterline the bow becoming much fuller in volume and flaring out like some retro american boats with one or more spray above the waterline.

However I must say that I am very confident with the seakeeping of my last two SD boats
and their heavy weather capability and you get used to the spray.
 
Bandit said:
I would say as a generalisation that semidisplacment are prone to be wetter than planing hulls due to the fact that a lot of semidisplacemnt hulls give a soft landing by not decellerating fast when thy hit the wave but having a fine entry and progressively burrying their bow in the wave.

Planing boats tend to have a wide full bow and spray rails to stop the bow burrying , this can give a hard landing.

The semidisplacemnt boats I have had 2 of Mitchel 31, a Halmatic 34 and an Aquastar 48 all tend to be a bit wet certainly the last two are the SD boats I have cruised extensively with and push the weather limits from time to time. They tended when you hit a wave to throw it up in the air and it either blows over you from the left or the right. I had a fairline 36 sedan, planing boat setween the last two sd's as a useful comparator.

Certainly bow shape will improve the dryness so a wide bow above the waterline with flare of bow turning the water away and not up will help.

Spray rails or steps above the waterline at the bow will turn the water away and down when you hit a wave.

So If I was about to design a hull for the ultimate Semidisplacemnt dry ride.

Fine entry to waterline, with spray rails below WL.

Above the waterline the bow becoming much fuller in volume and flaring out like some retro american boats with one or more spray above the waterline.

However I must say that I am very confident with the seakeeping of my last two SD boats
and their heavy weather capability and you get used to the spray.
Click to expand...

You mean something like this ....
 
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paul salliss said:
I am interested in owners thoughts on this and if this "wet" boat scenario has in any way put them of semi d style boats
Click to expand...
Well, of course SD (and even more so full D) hulls are bound to get more spray over the deck than any planing hull, at least assuming that the sea conditions allow the P hull to keep the speed it's designed for.

But I'm puzzled by your question: why do you think that this fact alone should put anyone off from SD/D boats?
Before my current (one and only) full D trawler, I had various planing boats, and I had to wash them as much as I have to wash this one.

Do you want a dry boat? Keep her on the hard, and under a shelter! :D
 
I think it has as much to do with where the bow wave is generated and where the helm station is situated as anything else. The bow wave of a planing boat is generated about 1/4 to 1/3rd of the hull length back from the bow so most of the time, the bow wave is picked up by the wind and falls behind the boat. In my experience, the further aft the helm station is, the wetter it will be. My planing hulled Broom 37 was quite a wet boat only because the design of most Brooms puts the helm station relatively far aft. With SD boats, the bow wave is generated further forward than with P boats so inevitably any beam wind is going to throw more spray on to the boat. Yes of course there are other factors such as the effectiveness of spray rails
 
This is my old girl punching along at about 12kts, she sucks down, makes a huge wake for a little boat, but she'll do it in appalling weather just the same except the wipers won't keep the screen clear, she's certainly what you'd call a wet boat, but not on the inside:D

009-2.jpg
 
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