Filling in rails on the hull - wave slap

[simonfraser]

Various threads suggest this is worth while and does not appear to affect the performance, much.
As i potter around i am not too bothered about the possible effect moving around.

Would like to fill in the rails at the waterline only.
GRP boat, what can i put on / in as a temporary filler that is relatively easy to remove but will stay in for a few weeks ?
The boat is on a trailer so easy to put some more in if it falls out.

Recon even duct tape or similar would hold at lower speeds, but leaves a gap at the front which will cause it all to tear off for sure

 

[jrudge]

Well if someone thinks it can be done an a squadron 58 with no ill effects I am all ears !

 

[MapisM]

Various threads suggest this is worth while

Define worthwhile.
In my experience, the day and night difference does NOT come from the hull shape (including rails, hard vs. round chines, whatever), but mostly from the material.
If you can't sleep with the wave slap noise, I'm afraid that a wooden hull is just the ticket.
With a plastic boat, aside from the practical difficulties of filling the rails, I would be shocked if you could achieve anything more than a very marginal difference - if any.

 

[simonfraser]

http://www.trawlerforum.com/forums/s3/slapping-noise-waves-hull-442.html

 

[MapisM]

LOL, it appears that the "more rum" solution garnered much more consensus than any hull adaptations...

 

[Bouba]

LOL, it appears that the "more rum" solution garnered much more consensus than any hull adaptations...

Yes, for us trawler men. For the planing boats I would suggest Buck's Fizz

 

[Blue Sunray]

I heard a suggestion that floating fenders alongside the hull can help, not had the need for it myself though.

 

[Nick_H]

There have been a few attempts at designing and marketing "slap stoppers", so may be worth a google.

 

[Murv]

The company in the states that designed the slap stopper does have a version for the bow of motor boats (the original was designed for the stern of sailing boats)
They were all set to take my card details and ship one to me, but then declined to give an actual cost so I (obviously) took it no further.

Incidentally, I'd tried everything with mine, fenders, foam noodles on a rope, even ply suspended with a float at the top and weighted underneath, all made zero difference so modifying the hull shape may be the best solution if it's really that important.

 

[MapisM]

modifying the hull shape may be the best solution if it's really that important.

Trust me, it isn't.
Sailboats have the best hull shape known to mankind for deflecting the water flow efficiently - in sharp contrast to P hulls, which are designed to climb over it and "fight" against it, sort of.
But I just spent one whole week sleeping in the bow cabin of a Hanse 47', and it would have taken instruments to measure the slapping noise difference vs. a GRP mobo - if any.
In my old mobo, with her 40mm thick planks, in the same conditions I had ZERO noise inside.
It is indeed that different.

 

[Bouba]

Trust me, it isn't.
Sailboats have the best hull shape known to mankind for deflecting the water flow efficiently - in sharp contrast to P hulls, which are designed to climb over it and "fight" against it, sort of.
But I just spent one whole week sleeping in the bow cabin of a Hanse 47', and it would have taken instruments to measure the slapping noise difference vs. a GRP mobo - if any.
In my old mobo, with her 40mm thick planks, in the same conditions I had ZERO noise inside.
It is indeed that different.

That begs the question, what would happen if you lined the front cabin with 40mm thick planks? (Other than never needing the trim tabs again)

 

[MapisM]

That begs the question, what would happen if you lined the front cabin with 40mm thick planks?

LOL, that's a good question.
Just go ahead and do it, taking lots of pics while you are at that - I'm sure it would make a great refitting thread!

Actually, gut feeling tells me that the problem lies with the fact that fiberglass is a very good sound propagating media, as opposed to wood which does exactly the opposite.
But some empirical evidence would be interesting anyway! :encouragement:

 

[BartW]

we discovered a partial solution just by coincidence,

it ocured to us that the last few seasons we didn't hear as much slapping noise than we were used to,
also guests in the Bow Vip cabin didn't complain as before,

in the same period, we are using the bilge space underneath the bow Vip cabin for storing, spare deflated fenders, old and spare ropes, (lots of them) and spare fender sock's, all items that have very good sound absorbing properties,
and apparently they seems to give a noticeable improvement on slapping noise.
I had in mind to post this experience a while ago.

so answer to OP,
try to place absorbing materials in the bilge space where the slapping noise is most apparent
you would need materials with some weight, like rubber or rope,
only light materials like foam is not good enough.

 

[Trundlebug]

Well we don't get ANY noise in our round bilged GRP displacement boat.
The silence is wonderful.

So I'm not sure it's all down to material, hull shape definitely makes the biggest difference.
As I find myself saying, she's built for comfort, not for speed. You can't have everything.

 

[BartW]

Actually, gut feeling tells me that the problem lies with the fact that fiberglass is a very good sound propagating media, ...
But some empirical evidence would be interesting anyway! :encouragement:

see my previous post :encouragement:

 

[BartW]

Trust me, it isn't.
Sailboats have the best hull shape known to mankind for deflecting the water flow efficiently - in sharp contrast to P hulls, which are designed to climb over it and "fight" against it, sort of.
But I just spent one whole week sleeping in the bow cabin of a Hanse 47', and it would have taken instruments to measure the slapping noise difference vs. a GRP mobo - if any.
In my old mobo, with her 40mm thick planks, in the same conditions I had ZERO noise inside.
It is indeed that different.

surprising observation P,
in several occasions I investigated the slapping noise on our boats, (on BA aswell on previous smaller boats)
and always' the slapping noise came from small waves that were "trapped" in that hull section where the chines reach the surface,

your old wooden tub doesn't have chines, so no trapps iirc

but admid that In have zero experience on sail boats.

 

[petem]

we discovered a partial solution just by coincidence,

it ocured to us that the last few seasons we didn't hear as much slapping noise than we were used to,
also guests in the Bow Vip cabin didn't complain as before,

in the same period, we are using the bilge space underneath the bow Vip cabin for storing, spare deflated fenders, old and spare ropes, (lots of them) and spare fender sock's, all items that have very good sound absorbing properties,
and apparently they seems to give a noticeable improvement on slapping noise.
I had in mind to post this experience a while ago.

so answer to OP,
try to place absorbing materials in the bilge space where the slapping noise is most apparent
you would need materials with some weight, like rubber or rope,
only light materials like foam is not good enough.

Personally I like the slapping sound of waves against the hull, reminds be that I'm on the boat!

As I may have mentioned, one of our refit projects is to fit A/C in the unlined locker under the forward berth. The other is to improve the engine bay soundproofing. A fellow forumite emailed me this morning and mentioned that engine bay soundproofing should be attached, where possible, to all of the flat surfaces in the engine bay (not just the hatch).

So now I'm thinking that I might line the sides and hatch for this forward locker with sound-proofing material which could eliminate the noise from the A/C unit and absorb the sound of waves slapping against the hull.

What do you think?

 

[kashurst]

it will all help but easiest solution is soft earplugs.

 

[BruceK]

it will all help but easiest solution is soft earplugs.

That's my solution. It even blocks out the dawn chorus of the kids. I get the longest lie ins on the boat and that's something to smile about.

 

[BartW]

As I may have mentioned, one of our refit projects is to fit A/C in the unlined locker under the forward berth. The other is to improve the engine bay soundproofing. A fellow forumite emailed me this morning and mentioned that engine bay soundproofing should be attached, where possible, to all of the flat surfaces in the engine bay (not just the hatch).

So now I'm thinking that I might line the sides and hatch for this forward locker with sound-proofing material which could eliminate the noise from the A/C unit and absorb the sound of waves slapping against the hull.

What do you think?

yes indeed for a engine bay, attach sound proofing to as much surface as possible,
and even more important, make sure that al hatches close perfectly with a rubber seal !

you could do the same around the A/C unit, and inside the some bilges

but pay attention that you don't create other problems,
for engine en A/C, check that air can flow where needed ( for ventilation or cooling)
and make shure that no heat parts (turbo fe) can touch the acoustic isolation
or foam get wet,
...

regarding sound proofing materials,
I saw some good advice in your rebuild threat, I have no personal experience with specific products,
but general rule is:
use matarial which is a combination of a foam and extra weight (rubber or lead ) layer inside.
the thicker the material (min 40mm)
and the heavyer weight /per m2
gives better the isolation

recently I have placed new acoustic foam in one genny (only 20mm, and only foam, no extra weight)
the isolation was only marginally better than the other genny with no foam
( Original old foam was pulverised due to age)
I have to add that the covers seals don't close perfectly anymore, need new rubbers !