Questions about building a fiberglass swim platform

[jy118lfd]

I have thought about building a swim platform for my boat, 24 foot single sterndrive walkaround. My transom is straight and I was going to just set the platform off the transom a 1/4 inch on stainless brackets. (Instead of bolting directly to transom.) I am mostly doing this for a few reasons. First safety, you cannot climb into my boat, if you fell overboard, as the freeboard is too high. Second storage for a livewell and maybe straping sharks to the platform instead of hualing them onboard. Third, I am thinking that the platform would reflect some sound away from the boat at cruise. Not that it is that loud but any reduction would mearly be icing on the cake.

Now to my question;
I have some experience with glass work but never built anything from a mold. I was thinking of building a mold out of melamine (coated particle board) and then just putting a small radius (fillet) in the corners to smooth the transition from horizontal to vertical surfaces. I am going to taper the front to back and also build the sides and rear to about 2 1/4" thick. I was going to use polyester resin The layup would be wax, PVA, white gelcote then 2 layers of 1.5oz mat, 2 layers of 1708, then a piece of 1/2" marine ply, two more layers of 1708 and then 2 more layers of 1.5 oz mat. I was then going to spray gelcote over the bottom just to seal it all up. I would then take it out of the mold and tape off the areas I did not want nonskid and texture roll some waxed gelcote to the top for nonskid. (This would match the nonskid on the boat. )

Am I missing anything? Anyone with fiberglass experience see anything wrong with this? Does anyone know how much resin I would need? Dimensions would be about 78" x 18" give or take the taper.

 

[ondarvr]

Re: Questions about building a fiberglass swim platform

The plan sounds fine.

To estimate the amount of resin needed, calculate the number of sq. feet of the glass you're going to use, then figure the total weight of the glass and double it. The mat will use double it's weight in resin and the 1708 will use closer to it's own weight, but there will be wasted resin, so you'll end up needing all of it. Resin is around 7 to 8 lbs per gallon so you can figure it from there.

 

[erikgreen]

Re: Questions about building a fiberglass swim platform

ondarvr is the man for resin info.

My only comment, other than that you seem to have a good plan, is to think over your layup (cloth ordering).

The 1708 has stitched mat attached, so what you're actually getting with two layers of it is biax-mat-biax-mat... putting two layers of mat outside that will not provide much in the way of strength, and will absorb a bunch of resin. I'd suggest if you need the thickness to just add another layer of 1708, maybe with a layer of surfacing mat. Or alternatively just skip it, two layers of 1708 per side is a lot of strength.

Make sure whatever perforations are in the glass get sealed, of course. The plywood core will soak up water and make you stern heavy (because of leverage) pretty easily. More generally, plan to check and adjust your fore and aft trip once the platform is installed.

Oh, and make sure you post pics of the whole process

Erik

 

[jy118lfd]

Re: Questions about building a fiberglass swim platform

ondarvr is the man for resin info.

My only comment, other than that you seem to have a good plan, is to think over your layup (cloth ordering).

The 1708 has stitched mat attached, so what you're actually getting with two layers of it is biax-mat-biax-mat... putting two layers of mat outside that will not provide much in the way of strength, and will absorb a bunch of resin. I'd suggest if you need the thickness to just add another layer of 1708, maybe with a layer of surfacing mat. Or alternatively just skip it, two layers of 1708 per side is a lot of strength.



Oh, and make sure you post pics of the whole process

Erik

The only reason for the mat on the bottom would be for water proofness. Mat is the best for this and I always thought 2 layers for the best water protection. Of course the 2 layers of mat on top (first) is to protect from print through.

 

[jy118lfd]

Re: Questions about building a fiberglass swim platform

The plan sounds fine.

To estimate the amount of resin needed, calculate the number of sq. feet of the glass you're going to use, then figure the total weight of the glass and double it. The mat will use double it's weight in resin and the 1708 will use closer to it's own weight, but there will be wasted resin, so you'll end up needing all of it. Resin is around 7 to 8 lbs per gallon so you can figure it from there.

Approx 10 sq foot

Mat
1.5 oz mat (per square foot) 15 ozs x 10 x 4 layers = 60 x 2 120 oz

Biax
25oz per sq yard
8.3 oz per sq foot x 10 x 4 layers =332oz

120+332= 452 / 16 oz per pound = 28.25 / 7 lbs per gallon 4 gallons resin

Is my math correct? Does four gallons sound right?

 

[erikgreen]

Re: Questions about building a fiberglass swim platform

The only reason for the mat on the bottom would be for water proofness. Mat is the best for this and I always thought 2 layers for the best water protection.

I think I speak for many of the experienced fiberglass folks here when I say......."What?!?"



Erik

 

[ondarvr]

Re: Questions about building a fiberglass swim platform

I don't think you doubled the weight of the Biax, so you may need a liitle more resin

 

[Mark42]

Re: Questions about building a fiberglass swim platform

How about making it from foam? If you use epoxy, then the pink rigid foam insulation at the home centers can be used.

Glue up a few sheets of the 1.5" foam board, then carve and sand to shape. Its really easy to sand and form. But not strong enough to support the glass if you will be walking on it. So after you carve and sand to the finished shape, slice it cleanly into three sections, (left, center, right) and trace the profile on plywood. Cut the ply and re-glue the three pieces with plywood between. That will give it some vertical rib support. Then 4 layers of 1708 and it will be tough as nails.

Just a thought. Thats how I'm making the hard top on the Bayliner in my signature.

 

[jy118lfd]

Re: Questions about building a fiberglass swim platform

I think I speak for many of the experienced fiberglass folks here when I say......."What?!?"



Erik

I was always told and even read in a couple of fiberglass books that Mat, having the qualities that you stated (very resin rich) made it the most water proof of the different fabrics. So I always finished up with 2 layers of mat. I do not think you would need this on the inside of a boat or with epoxy.

I would be putting the mat towards the wood core for adhesion so i would end up with the roving facing the outside. It would be easier to finish it off if there was a layer of mat or two before gelcoat on the bottom. I am not looking to build up the strength as the 1708 would do that.

 

[a70eliminator]

Re: Questions about building a fiberglass swim platform

Mark I saw a program on the TV a few weeks ago it's called (how things are made) anyhow they did a segment on surfboards very similar to what your doing only I don't think they used anything other than the foam cut with a hot wire to shape then applied layers of mat and resin with the vacuum bag method, now I'm not sure and I wish I had payed better attention or taped the episode but It mignt have been a carbon fiber material rather than plain fiberglass. I don't know anything about surfboards other than a shark can bite it in half, It seems like one would be lightweight and strong enough if supported properly to work for a swim platform, I'm not at all saying an actual surfboard would work, just comparing building technique strong and lightweight, If I built one from plywood I'm afraid it would end up too heavy combined with it hanging off the stern mignt have ill effects.
Well anyhow just some material to think about to keep the thread going.
I'm poor $1500 bucks doesn't come easy for me.

 

[jy118lfd]

Re: Questions about building a fiberglass swim platform

I think Plywood is a great boat building material. Its heavier than the newer foams and such. But it is easy to work with and lasts a long time when properly sealed. We're not talking about a 4x8 sheet of 3/4 but approx 24" x 80" of 1/2. I don't think using an exotic material is going to really cut the weight that much. There is not that much weight there to begin with. Especially when the bulk of the weight in this project is in resin and glass.

4x8 sheet of plywood is about 25 lbs per 1/4 inch so a 2x8 sheet of 1/2 is about 25 lbs. Even if you took that out completly its only 25 lbs of savings.

I can sit (235lbs) on the transom and not make the scuppers touch the water. Unless I go to one side. Besides I need a little weight in the stern as I load the cabin with s%$t and it just seems to collect there.

 

[jy118lfd]

Re: Questions about building a fiberglass swim platform

I don't think you doubled the weight of the Biax, so you may need a liitle more resin

Yeah you are right looks more like 6 to 7 gallons.

If I add all the parts up in weight I get

40lbs of resin
20 lbs of glass
25lbs 1/2 ply

Approx 85 lbs for the Platform.

I am just trying to get an Idea on how much weight I am going to add. Its not really that much weight at all. When I am done with it I am going to weigh it and see how close it is.

 

[Mark42]

Re: Questions about building a fiberglass swim platform

I think Plywood is a great boat building material. Its heavier than the newer foams and such. But it is easy to work with and lasts a long time when properly sealed. We're not talking about a 4x8 sheet of 3/4 but approx 24" x 80" of 1/2. I don't think using an exotic material is going to really cut the weight that much. There is not that much weight there to begin with. Especially when the bulk of the weight in this project is in resin and glass.

4x8 sheet of plywood is about 25 lbs per 1/4 inch so a 2x8 sheet of 1/2 is about 25 lbs. Even if you took that out completly its only 25 lbs of savings.

I can sit (235lbs) on the transom and not make the scuppers touch the water. Unless I go to one side. Besides I need a little weight in the stern as I load the cabin with s%$t and it just seems to collect there.

I didn't suggest foam for its light weight, I suggested it because it is easy to work with and lets you form it easily into pleasing shapes. Much easier than you can with wood.

I think that plywood is a good product to make a swim platform from too. And you can have the best of both materials. Build the basic plywood platform, but make the sides and trailing edge about 3 inches short all around. Then glue up some foam boards (the pale blue is compatable with polyester resin) to the edges about 3 inches thick, and then round them off so there are nice rounded, curved sides to the platform all around. Then apply the glass as you planned. You end up with the strength of the plywood, and the nice rounded edges that look nice.

BTW, check out fiberglasssite.com for their resin coverage by glass type/weight. Very useful. I bought from them, and their estimates were right on the money. Also take them up on their offer to call and discuss your project and get their suggestion on what glass and resin is right for you. They were very helpful when ordering for my hard top project.

 

[jonesg]

Re: Questions about building a fiberglass swim platform

I see teak platforms on craigslist for $200 all the time.
You can't beat success.

 

[rtpassini]

Re: Questions about building a fiberglass swim platform

why are you guys adding so much weight to this thing? 2 or 3 layers of mat should be plenty.

 

[jy118lfd]

Re: Questions about building a fiberglass swim platform

I see teak platforms on craigslist for $200 all the time.
You can't beat success.

I have seen a few too. But I just can't get past the fact that teak would look horible on my boat.

 

[a70eliminator]

Re: Questions about building a fiberglass swim platform

Mark I think it's a great idea to use plywood for the structure then finess the edges in foam then glass over the whole thing, it would come out looking more stylish than just a flat shelf.

118 I think you have a great plan with fillet transitions and all I'll bet it comes out nice whatever you decide. and by the way if visit swimplatforms.com there are nice specimens with pics of the undersides and mounting ect. but you'll have to browse their site for a while to find them.

 

[ondarvr]

Re: Questions about building a fiberglass swim platform

Plywood works well for this type of application, a high density foam, or Penske board type product would work well also, some don't even use a core, just a few ribs to stiffen it, so there's many ways to do it.

It probably doesn't need that much glass, but swim platforms can really take a beating at times, so if the weight isn't that big of a deal it won't hurt anything.

Surfboard foam is pricy stuff and so are most of the other core materials that would take the place of plywood and while marine ply is good stuff I? don?t think it's necessary for this project.

If all the holes are sealed well it should last longer than the boat.