Water creeping up hullsides

The Redfin was launched in September of 2022 and underwent major changes, many thanks to @Ad Hoc and @baeckmo . This boat is the Skoota 32 demountable designed by Richard Woods. It is performing fairly well, but for this issue and any quartering or sharp head seas are harder due to the boat being light (on purpose).

Ad Hoc helped me with a serious hull problem and we added bow extensions. The boat is running perfectly in calm seas, balance is good. We were running 22.4 kts before adding some fixed plates last week. But the boat needs one more issue addressed.

In late October in Mobile Bay, the Redfin got a taste of the sea, and it was pretty awful, but mostly because the boat was in head seas on a plotted course that was 12 miles and I originally thought it was 2. So, I learned to use the autopilot. And then November 2/3, the boat had following seas and ran 16-19 kts steady for 232 miles all the way about 10 miles offshore at times using the autopilot. Performance was decent, 1.7mpg, but for some annoying water blasting into the cockpit in the spaces between the bdeck and hull, and a bit of spray hitting the windshield.

I also had a horrid spray coming off the hulls related to buttocks and engine distances back. This was also corrected with the help of @baeckmo and we tested it Sunday as well. The boat gained over 1 knot of speed! And the goofy shower off the engines is gone. On flat water, it ran 23.6kts at 5700rpm. Probably could run a different prop to get some more speed, but not needed.

But this problem of water creeping up the hullsides must be fixed.

@baeckmo gave me some best guesses, but Sunday I made a video and am wondering if anyone has any further advice. Bodo did not see the video, yet, and I was worried his idea was going to be too far back to be effective, but have not discussed with him; to be fair.

The video is 3 minutes long. At about 50 seconds; you’ll witness the problem at its worst, where water blasts up the hullsides and into the cockpit with a force that might knock someone over. The water is basically getting funneled through about a 1-2” gap; think powerwasher. You won’t see the location or the blast on this video, just the action of the water.

I do have access to the chine seen in the picture. The outsides of the hull do the same thing and also causes the boat to run a bit wet.

I made some 4’ long wooden spray rails, but they seem too short for what I see in the video. The hullsides are not flat enough for angle irons. I already know an 8 foot long wooden spray rail won’t bend enough on the horizontal section as well.

Stand by for you tube link.

 

To be clear, noone has seen this video and all prior discussions were with less knowledge. Thanks for any replies.

I’m thinking some type of splash rails. The chines have extra tabbing and probably about 75oz glass outside, 12mm San Corecell M, 100oz glass inside, triaxial and 1708 tabbings

At about 50 seconds, a LOT of water blows into the cockpit.

Also, the crimson paint is painted 3” above the designed waterline and we might be a bit below lines, but not much.

 

The image is provided to show the chines. The inside of the hull is not accessible at the lower chine and that is below dwl anyway. Image is copyrighted. I will delete them tomorrow.

@Richard Woods

Hope it is okay to post this drawing. I probably ought to have asked first.

I’m thinking perhaps I can intercept and deflect the water at the chine which is accessible from inside for bolting, etc.

 

Ok Dan, glad the "engine flaps" worked as planned (looking forward to some images); the side-wetting problem is very common issue. It is not only a nuisance, causing a wet ride as you mentioned earlier; it will increase drag as well. Even in flat-sided tunnels there will be water climbing vertically if no horizontal fence applied. Most of the cats I have built are of this design, and I always use spray rails in along the full WL on the tunnel sides.

As far as I can judge from the available info, your Scoota is attaining higher speeds than it was designed for (correct me if I'm wrong!), and she certainly should have rails in the tunnel (and probably along the P+Sb sides as well). I'd aim at something like 50-60 mm wide, attached about as much above the WL from bow to 2/3 WL length.

On top of that one, you add a second, ~150 mm above (at its aft position) and with a 3 degree "bow-up" inclination, length from bow to front of center body.

 

For a quick test, buy some PVC trim about the correct dimensions at the hardware store, you can easily shape it with wood working tools, and it bends to a custom fit with a little heat. Use two sided tape to attach it temporarily to the hull, don't use the really good 3m tape for a temporary test, it may work for a more permanent test though.

This will be cheap and quick to see what works and where it needs to be located. You can use it like that until you make something more permanent.

 

A few comments/questions.

First, thanks.

Second, I have antifouling paint 75mm above dwl, so anything I stick on must be there or above at the lowest or ain’t gonna stick, and there is no mechanical fastener access. The entire area is in watertight compartments and very buried.

Third. What sort of profile? I built some 4 foot long wood spray rails with a seat and interlock. They were going to be about 70mm out net, but they don’t make the hullshape over a longer distance and they are too short, so fancy firewood now.

I have in stock 24mm corecell M60 or M80. I could epoxy bond them up into a bendable profile and seal with epoxy and paint even, then bond with 5200.

I’m not sure I need to go much further back than the end of the bdeck. The cockpit is 7” higher and it has never had water hit it even in really big channel/bar waves. So, roughly 24 feet max. The original waterline was 32 feet. I’ll need to be careful not to go above the chine. If I start out at say 80mm above dwl, according to the drawing above, I’d have 940 minus (390+80) or 380mm in 24 feet, measured from the bottom. Less the profile base, say 80mm. So 300mm in 24 feet is only about a 2 degree upsweep starting touching ?. Unless the 3 degrees is more important and the 2nd rail is shorter? Or my no drawing math is off.

And the biggest question is the profile. A square profile is fast and easy and ugly as hell, but offers a lot of glue area at say 75x75. A triangle will send water up in the air.

My two piece interlocking wood thing was a 2.5” flat base with angles down to 1/8” thick and a lengthwise dado about 1/4” deep and the horizontal piece was 1/2” thick and would fit into the dado. But not bendable as built. If I need 24 feet times 8, I need to produce 200 lineal feet of it, and I sold my router table for the move to Texas.

Anyhow, profile advice is welcomed.

 

What about this profile?


I could glue up corecell 25mm times 3 at say 80mm wide, then tablesaw rip the stuff to get the triangle and double the quantities.

 

Here are the fixed trim tabs. The spray issue is 100% gone. Was surprised to see the speed pickup.

This boat was designed to achieve 20kts or a bit more. The bow extensions saved it.

 

I have a limiting factor to the spray rails. There is a lightning bar at the bdeck, so they are going to be shorter. They will end at the bdeck/lightning bar.

They will still be 20’ long.

 

Port side view.

 

Hi Dan,

As noted some time ago, we had similar issues on some of our high speed cats many years ago., It was execrated when we built some of them in composite. The issue, as you described, but on one of our vessels was even worse. On a flat calm day running at 25knots the spray coming off the bow, and sides at the stem was causing spray on the wheelhouse…it went that high up, and on a flat calm day. The issue was the stagnation point created on the bow by being composite.

The stem was too bluff, as are all composite hulls, for obvious reasons. Our solution was to add a very sharp stainless plate, that literally “cut” the water flow at the bow. It was about 200mm above and below the dwl at rest. The plate is ostensibly a V shape plate that fits around the hull. The apex of the V is ground to a very sharp point, almost like a razor.

Shown below:



This cured it instantly.

So, it would be worth getting – if possible – views of the bow, from another boat, when you’re at speed to see if this is also your issue. Not just being created on the BB but also the stem line.

 

On light inshore chop, I don’t get any spray at all.

I could run the camera the other way and point it to the front and do another video, but need to leave in a couple days and the wind and waves offshore are rather high now. I normally won’t go out if seas are 1M or above.

So, @Ad Hoc , is your suggestion the bow is dipping and the stem is not cutting, but water sort of wraps around it? The bbs are sharp, as you instructed, but the main hull stem is rounded. I did not sharpen it even with thickened resin. It was just faired with a form and is probably about 1/2-3/4” radius semicircle.

 

That's what I suspect, hence a front view would be useful.