Building a shroud - Any advice?

[EricJRW]

My 50HP 2-cycle Evinrude really puts out a lot of noise... So much so that the aft seats are not a fun place to sit while underway, yet those are the best seats in the house (comfort and under the bimini). In the grand scheme of things, I don't think the motor is louder than it should be, it's just that the proximity to the aft seats is bad.

So I came up with the idea to build a shroud... Basically a four-sided box with walls on the sides and in front of the engine (between the engine and the aft seats) and fit it with a hinged top.

The height will be such that I can tilt the motor up fully without having to lift the lid on the box, but the lid is hinged (at the front/fore edge) to allow access to the motor.

It will be 51" wide, about 28" front to back, and about 30" high. I can get all this out of a single sheet of plywood IF the front is only 20" high (meaning there will be a 10" gap at the bottom, directly behind the rail and aft seat, which I figure will also absorb/reflect a lot of the sound).

I could eliminate the gap if I wanted to lift the lid when I raised the motor, but since we beach the boat every once in a while, I wanted to be able to keep the top of the box flat for a place to tie a tube or other light objects.

Since I'm still not 100% on the height, I decided to build a prototype out of exterior grade plywood instead of the more expensive marine grade. I figure if I get one season out of it, and prove the concept, I will build the next one out of marine grade, seal it, and cover it with carpet.

So what do you think? Is there anything else I should consider?

Thanks for reading,

Eric

PS. I've attached two pictures of the stern of the boat. The shroud will basically be the size of the aluminum deck, i.e. it will fit between the two carpeted areas and go from the back rail to the back of the boat. The height will be to the top-most rail (I think a good height for stowage too). If I went to the lower rail, the gap at the bottom would not be required, but then the lid would need to lifted to tilt the motor all the way up (the boat is kept out the water at our dock, so tilting is not strictly required to dock, just to beach).

 

[EGlideRider]

Re: Building a shroud - Any advice?

A couple of guys in my previous boat club had done exactly what you are talking about with good results. I don't remember any details however.

IMHO, I'd build it only once. It's gotta help and it certainly won't be any noiser. I would use exterior grade plywood and seal ONLY the top side of the top piece and both sides of the vertical pieces. Do NOT seal the bottom of the vertical or horizontal pieces to allow any trapped water to escape.

I would put carpet on the outside pieces and aluminum covered insulation on the inside part of the box.

But remember, these remarks are as stated... IMHO.... LOL and good luck.

 

[EricJRW]

Re: Building a shroud - Any advice?

I like the aluminum covered insulation idea! Thanks for that!

Oh, and good tips on sealng too!

 

[lmuss53]

Re: Building a shroud - Any advice?

I've seen a few people close that whole stern area off with a sundeck setup with sides that isolate the motor and protect batteries and fuel tank. I've seen aluminum frame and plywood combos that really turn out nice. The 1" square framing tubes and hardware are available at Lowes and other building centers. Do a google on "homemade sundeck for pontoon boat" and you'll find a few. A big thick sundeck pad will really knock down the 50 noise and make a nice addition to the stern.

 

[EricJRW]

Re: Building a shroud - Any advice?

Yeah, I saw that one... Very impressive, but a bit more than I want to bite off right now (also more $$$). Don't really need a sun-deck, but I did like how the construction was 100% weather/water proof. If this pans out, maybe I'll do more down the road.

 

[srimes]

Re: Building a shroud - Any advice?

back off the throttle.

 

[EricJRW]

Re: Building a shroud - Any advice?

back off the throttle.

Well top speed is 20 and sometimes we just got to get to where we are going.

 

[PGFISHER]

Re: Building a shroud - Any advice?

I've seen a few people close that whole stern area off with a sundeck setup with sides that isolate the motor and protect batteries and fuel tank. I've seen aluminum frame and plywood combos that really turn out nice. The 1" square framing tubes and hardware are available at Lowes and other building centers. Do a google on "homemade sundeck for pontoon boat" and you'll find a few. A big thick sundeck pad will really knock down the 50 noise and make a nice addition to the stern.

I did almost exactly that to mine and the noise is no longer a problem. I split the deck into 3 sections; one for the engine and one each for the side decks. I have a rear entry on the starboard aft, so I made that side hinge all the way over so that it folded flat against the side. My wife loves the combination of sun deck and quiet.

 

[lmuss53]

Re: Building a shroud - Any advice?

The google didn't turn up much. I've got a guy on a different forum looking for some pics of his simple sundeck project.

PG got any pictures of yours? This might be something I'm interested in doing on my 19 foot boat.

 

[EricJRW]

Re: Building a shroud - Any advice?

This is the one I know of (by "ralphl"), and it looks very good:

http://forums.iboats.com/showthread.php?t=421884

I don't think sound was not the priority on this project, but I think it could be modified for sound and it's a very robust design (just too robust for me).

 

[mfwyatt]

Re: Building a shroud - Any advice?

I am going to do the same thing to mine. Here is an example from a local marina.

 

[Silver Eagle]

Re: Building a shroud - Any advice?

I have a 24 ft Starcraft that already has what you want to build. I posted pictures of it some place on this site. The cover also swings over so that if you want you can add oil to the engine. if needed. Just by swinging the top back .What I do is lift the front cover and it folds back out of the way .It's on two bolts only. I can also check my battery and fuel the same way. Try midlanticmarinecenter.com and look at there new boats. Maybe one of them has what you want in design. Maybe the can send you information on one. look at page 3 "Home made boarding ladder". There's a picture of the rear of our boat.

 

[robert graham]

Re: Building a shroud - Any advice?

I wonder if you could start with about the right size cooler and cut out the areas as required, add foam insulation on the insides, hinges, latches, whatever, paint cooler to match boat or to disguise it "from being a cooler", might be an idea, and coolers are already waterproof and some have 2 inches of insulation! Just a creative idea...

 

[sasto]

Re: Building a shroud - Any advice?

I built one for an 18 CC fish boat out of closed cell foam and CSM to keep the weight down. I faired it with filler and gel coated it. Hinged it on the splashwell with a piano hinge. I kept it low profile and attached a piece of bunk carpet above the motor. The box would tilt back with the motor. Amazing the difference by deflecting the noise from the outboard.

 

[river critter]

Re: Building a shroud - Any advice?

My uncle had the same problem with his 48spl . He had a heat and air place in town that builds ductwork build him a cover made a big difference. Cost him about $50 . The only thing is he should have let it go back as far as possiblie along the top and the sides to push the sound out the back. Add some 3 inch pipe standing up to the corners for cup holders.

 

[luckyjr]

Re: Building a shroud - Any advice?

I think that is a good concept, use the proto to find the design. When you find that design, you might think about Homasote. It is a sound barrier product that comes in 4' x 8' about $35.and used in generator enclosures. There is an aluminum plastic clad called dibond that would make it look sharp and help with the water proofing. Have fun and take care.

 

[EricJRW]

Re: Building a shroud - Any advice?

Well it's been a while, but I built the box this past weekend... Only problem is when I finally took the boat out I learned ethanol has apparently fouled my fuel lines and now I'm replacing those (I already did the large lines, this weekend I will do the small). The box came out well.. I don't know how well it works yet, but the only problem I have not solved it how to keep the hinged lid down. For now I'm just screwing it... But I'd like a tool-less solution. I don't want any sharp bits protruding, and it seem elastic cords won't last, so for now I'm still scratching my head on this one. I was thinking of the type of fasteners used on muscle car hoods, but that seems overkill. Any ideas?

Here's a couple of pictures:



PS. Carpet and additional insulation may be next.

 

[MH Hawker]

Re: Building a shroud - Any advice?

I have been thinking of making one from the blue foam insulation stuff and glassing the out side of it to keep it light weight and making it to sit in brackets to remove all of it to access the motor if needed.

 

[EricJRW]

Re: Building a shroud - Any advice?

Brackets idea is nice. To either size of my motor is an L-shaped piece of metal (with hole already in the vertical part). The 15/16" plywood sits on top of that. I have to back out a few screws, but there is actually enough room for me in the shroud to work on the motor, which is good, as now I need to.

Only problem I had to solve was there that there was quite a bit of side to side motion. I put a couple of blocks of wood on the front of the box that fit inside the rails. This completely stopped the side to side motion.

The foam is a good idea. I was originally thinking going a little thicker on the plywood, but I was surprised how much heavier 3/4" is. I did not want to add too much weight to the back.

 

[muskiemike12]

Re: Building a shroud - Any advice?

This sould keep it closed. Cheap and simple.