Hull Slap

We have a queen island berth forward and the waves slapping on the hull are annoying. Was thinking of spraying a can of car undercoating on the inside of the hull to deaden the sound. Has anyone tried this, or have other solutions? Thanks.

This is a very common problem with a bunch of solutions proposed and/or tried. The only really successful one seems to be to fill in the spray rail around the waterline which is the source of the problem. That or earplugs.

My Chris used to have that noise. I learned to like it. It meant I was on the water and the sea was mild.

pete

truant2 said:

We have a queen island berth forward and the waves slapping on the hull are annoying. Was thinking of spraying a can of car undercoating on the inside of the hull to deaden the sound. Has anyone tried this, or have other solutions? Thanks.

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As already stated, this can be a problem with many models of boats, including Nordic Tugs. There has been much discussion on various NT forums, and the general feeling is that the only solution that has a worthwhile impact on the noise, is filling in (relatively expensive fibreglass work) the waterline splash chine. Everyone who has done that work on their NT has stated that it works and makes a huge difference.

Many other solutions have been tried from applying various forms of insulation to the hull interior and/or various floating temporary barriers to interupt the wave contact. None of those have shown much if any success.
Like Pete, I "sort of" got used to it, used ear plugs, and on those nights where it was horrible, slept in the salon.
If memory serves me, the cost most people mentioned was over $5,000.

On NTs (and the very similar ATs) I wonder if there is a market for a cheap solution. Say $500. This is quite doable, and might even be economically doable as there are so many identical hulls out there.

DDW,
I am sure that if someone could come up with an inexpensive solution that was effective, cosmetically looked good, and did not affect performance, they would sell a lot of "them".

Pete Meisinger said:

My Chris used to have that noise. I learned to like it. It meant I was on the water and the sea was mild.

pete

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They are normal boating sounds. Love or hate boating.

My boat has pretty bad chine slap. It's barely audible in the aft cabin, but significant everywhere else. I'm used to it at this point. On a boat that's capable of planing, you'll lose some lift and performance by filling in the chines. Plus you may take more spray at higher speeds.

Before you try car undercoating, give it the sniff test in an enclosed area.

What if you slid a tarp down the stem and walked it back on each side of the boat and pulled it tight enough that it made a smooth surface from the keel to the spray rail ? It would be a hassle, and look silly...... I guess it depends on just how annoying the noise is.

If you haven't seen it already, you might find this thread (and thread within this thread) interesting...
https://www.trawlerforum.com/forums/s53/hull-slapping-chine-53621.html

Pete Meisinger said:

My Chris used to have that noise. I learned to like it. It meant I was on the water and the sea was mild.

pete

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Yes and when the sound/frequency increases it's time to get up and take a look outside.

rslifkin said:

My boat has pretty bad chine slap. It's barely audible in the aft cabin, but significant everywhere else. I'm used to it at this point. On a boat that's capable of planing, you'll lose some lift and performance by filling in the chines. Plus you may take more spray at higher speeds.

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The only part of the spray rail that causes a problem is the part about 6" above to 6" below the waterline. On my (typical) boat that is a length about 3' long or a bit less. It is going to be out of the water when planing. The owners who have filled it in report no difference in performance or spray. Reportedly NT has modified their mold for the 37 to eliminate it on new boats.

The fix I am thinking of is a fiberglass or plastic molding, fitting in the spray rail groove, tapering from nothing to nearly full at the waterline to nothing again, about 3' long. You would scuff the area lightly and bond on with 5200. Installation would take an hour or two, they would be removable if you really hated them. There are several hundred NT32 and NT37, and at least a few hundred AT34/365, so the market is big enough. It is a perfect application for plastic molding, but for the tooling required. A fiberglass part of this shape is a bit tricky to produce inexpensively. I may be doing this for my boat in the next couple of months.

Benthic2 said:

What if you slid a tarp down the stem and walked it back on each side of the boat and pulled it tight enough that it made a smooth surface from the keel to the spray rail ? It would be a hassle, and look silly...... I guess it depends on just how annoying the noise is.

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reading this thread yesterday, that's close to what popped into my head.... but instead of a tarp I was thinking something a little thicker to absorb the vibration energy or dissipate the water....kinda in the spirit of a gym mat/pool noodle/boat fender......

We have a planing hull and we have slap nearly all the time. I have discussed this here, there and everywhere. There are lots of down-home solutions with a variety of results. Very few, if any, really work. You really just have to get used to it or move to a slip with less wave action. It will take a while to be sure. Another point was that I felt that with all the dangerous noises that could happen overnight, I refuse to wear earplugs. You will get used to the slapping eventually, but if a bilge pump goes off or some other noise happens that is out of the ordinary, your brain has a better chance of bringing it to your attention.

I just imagine that I'm on a boat.

skyhawk said:

reading this thread yesterday, that's close to what popped into my head.... but instead of a tarp I was thinking something a little thicker to absorb the vibration energy or dissipate the water....kinda in the spirit of a gym mat/pool noodle/boat fender......

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Good suggestion, however, it has been tried, using several different methods, and has failed to address the problem. Plus trying to keep the "device" in place is almost impossible. One person even devised a system using ropes passing under the hull that had to be "fitted" when on the hard to try to ensure that the "pool noodles" stayed in place. It required someplace to store wet, sometimes covered with weed, equipment, was very difficult to deploy and results were not great.
I tried a floating device, not with the ropes under the boat, using small weights to try to hold it in place. We tried it a few times and just gave up on it.

firehoser75 said:

Good suggestion, however, it has been tried, using several different methods, and has failed to address the problem. Plus trying to keep the "device" in place is almost impossible. ........it.

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well that's why I didn't bother to reply with the thought initially, and only as a reply to echo benthic2's idea with a twist for brainstorming purposes.
Just strikes me as something that could maybe be done successfully but a bigger pain in the neck regardless. Even if a person were to develop a similar idea into something easy to deploy and that would stay in place, you still have issues with marine growth, stowing it, etc....

more brainstorming......

What if you anchored/moored off your stern ? You could try using 1 cleat so the corner is facing the weather, or use a bridle to take the waves straight on. You might get slap under the swim platform but you are at the other end of the boat so it might be a little less annoying. Obviously not a solution if heavy weather is expected, but testing it out would be pretty easy.

Pete Meisinger said:

My Chris used to have that noise. I learned to like it. It meant I was on the water and the sea was mild.

pete

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Amen!

May I suggest, without any knowledge or experience, stern to the wind or perhaps quarterly?
At the dock, bow in.

Hull slap is a fairly common discussion on Nordic Tug forums. I purchased a new Nordic Tug 32 in 2006. The first night on my mooring, the slap was enough that I needed to do something about it. Anchoring off the stern, while it may quiet the slap, is not appropriate in any kind of weather. I put together a "hull slap preventer" described in NT forums, a pool noodle encased in sail material, strapped to the hull. Effective, but a PIA to deploy and remove. I contacted Nordic Tug, since they have the hull molds, and asked if they would produce a dense foam block that could be glassed into the chine. Response was "absolutely not". The following year I filled in a 4 foot section of the chines. That solved the problem, with no impact on performance or wave deflection at speed. Since I did the work myself, the cost of materials was only about $500 (CoreCell foam, epoxy resin, bonding material, carbon fiber tape, gelcoat). Boatyard labor would drive the cost up several thousand dollars. I know several NT owners who have spent $3,000 to $5,000 to have the work done professionally.

I like the idea from DDW of a fitted fiberglass or plastic molding that could be attached with 5200, or glassed in. Just like attachable spray rails for downeast boats, a molding is a viable solution. Here again, you would need a mold of your specific hull and proper placement, to produce that molding.

As a one-off, I could just take a splash off the hull, fill with foam, shape and glass the outside. Producing them is a little trickier - has to be a two piece molding glued together, or a plastic injection molding. Might be able to do it as a urethane casting. I'm figuring the market to be maybe 50 units at best for each hull, so a plastic injection mold is too expensive to amortize. It would be a pretty good application for 3D printing, except that is a really huge 3D printer.

Once one determines the proper placement on the hull, perhaps attaching rubber rub rail material??

Placement on the hull is pretty easy, spray rail at the water line. Probably anything stuck there would break up the slap on that flat surface, but it needs to stay there and not look horrible.

DDW said:

Placement on the hull is pretty easy, spray rail at the water line. Probably anything stuck there would break up the slap on that flat surface, but it needs to stay there and not look horrible.

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So paint it the same color as the hull. "Staying in place" is a matter of mechanics.
Perhaps the key is to make it duel purpose, reduce slap while at rest and reduce the spray while underway.

Chine slap

We have perfected what we call our quiet chine, which can be retrofitted to an existing hull. If you reach out to me privately, I would be happy to discuss.

truant2 said:

We have a queen island berth forward and the waves slapping on the hull are annoying. Was thinking of spraying a can of car undercoating on the inside of the hull to deaden the sound. Has anyone tried this, or have other solutions? Thanks.

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This is only a problem on boats with the master cabin as a V-berth. Next time, get a boat with an aft cabin and problem solved!

No matter what you do, there will be times when you encounter hull slap noise - depends entirely on the height of the wave-lets. Perhaps some soothing music for a relaxing background noise that will blend in with the hull-slap.

I had Swift Trawlers, 34 & 44, both with significant hull slap. Annoying when anchored in relatively quiet conditions, but small waves would cause resonating sound in fore cabin. Experimented with several “slap stoppers”, initially with pool noodles, finally with custom made foam “boards”, 6 ft. long, 12 in. wide, 2 in thick, covered in black Textilene, shaped to hull profile. Took 2-3 minutes to deploy, running lines from waterline at bow to stern, with slap stoppers positioned right where chine hit waterline. Curve of hull kept them snug against bottom. Reduced noise by 80%. Wife loved them, so did I. Practically invisible from outside boat. Very easy to deploy and retrieve, stored in chain locker. Total cost well under $50. Can supply pictures if interested (I still have them, for my next boat!)