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Old 01-27-2009, 06:39 AM
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Default Building a Fiberglass swim platform

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.
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Old 01-27-2009, 10:46 AM
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Default RE: Building a Fiberglass swim platform

Quote:
jy118lfd - 1/27/2009 6:39 AM

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.
Hello, I have done dozen or so boarding platforms and would be glad to help you with some of your questions.
The laminate schedule is about right to load a half-inch piece of marine plywood with just a little bit too much mat on the bottom. I think you could build a stiffer and lighter platform by utilizing a thicker and lighter core and a slightly different laminate. Before we spend much time on that, I would need to know the width of the platform ( port to starboard), the length ( for an aft), and the number of brackets.
Partially because most of the boats that I work on are stored in the water full time, most of the platforms that I make are not supported by stainless steel brackets but instead molded fiberglass brackets. But that's just a preference and they can successfully be built either way. I don't have very many digital photos ( I have a ton of 35mm) so this is the only platform that I have photos of and it's not very similar to what you're doing.
These photos don't even highlight the platform as the job was to firm up the chines, build a platform, a crab tank, and installed trim tabs. In fact the platform isn't completed yet, the color you see is the non-skin color, the edge will be gel coated hull color and a stainless steel trim will be installed around the perimeter.





You suggested a 2 1/4 inch flange around the perimeter which will give you a lot of stiffness, I had to be more conservative on the platform above to match the guards forward of it.
I build a lot of one of components and don't typically build as fancy of a mold as you're suggesting preferring instead to work with quick built particleboard forms. You have suggested that you were going to nonskid the surface after fabrication, leaving only a small amount of area that requires a high level of finish. If you build a fair product in a temporary mold it is not difficult to handle the cosmetics on a project like this.
If you can provide some dimensions, I would be happy to continue this conversation.





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Old 01-27-2009, 11:01 AM
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Default RE: Building a Fiberglass swim platform

call scott at silverhawk boats in nj don't have number with me he already has a mold for the 24 silverhawk he built me one all fiberglass no wood .
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Old 01-27-2009, 11:06 AM
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Default Re: Building a Fiberglass swim platform

I am looking toward 76 to 80 inches wide in the front and tapering back about 2 to 4 inches narrower in the rear. (I have not determined the taper as I want to build a template and mock it up first. The platform will be about 18 to 20 inches long (again depending on asthetics). I really wanted the 2 1/4"flange because with the out drive and trim tab I did not think I could get the platform as low as I wanted. This would give the profile the apperance of being close to the water line. I did not even think about the rigidity it would give.

The mold I was going to build is particle board just coated with melamine. (poly does not stick to this even if you don't put mold release on it.) I wanted a nice smooth radius in the corners for asthetics but if it can be done with out the fillet It would make it easier to make.

I was thinking about 4 stainless brackets. I just did not even think I could get it perfect enough to bolt the platform to the transom. I figured it would be easier to bolt on some brackets and then bolt the platform to the brackets. Plus I did not want to do any glass work to the boat.

The platform in the pics is about exactly what I want without the molded fiberglass bracket. Nice work!!!!
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Old 01-27-2009, 12:13 PM
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Default Re: Building a Fiberglass swim platform

76-80 inches wide and four stainless steel brackets... if you had 10 inches cantilevered on each side, your unsupported square is just over 18 inches x your length, which is a pretty small square and the plan that you proposed would work fine. I do believe it could be made lighter and I find 18-20 inch boarding platforms to be too short( keep in mind that you have a 13 transom angle that uses up some of that space) and I prefer 24-27 inches with some that I've built go to 36 although I realize that wouldn't fit your boat. Your boarding platform should accommodate you laying on the platform in order to clear a fouled propeller or replace one.
One of the reasons I push these crap boxes is that they help prevent an inflatable or skiff from getting under the platform while you're loading or unloading.
I would still suggest a thicker and lighter core and a laminate with less mat on the bottom. This is not necessarily the ideal place to use a double bias fabric ( I am a fan of double bias when its expense can be justified), a mat / roving laminate would be easier to handle on this project.
As to the anesthetics, it sounds like you're on track, I like a lot a radius on the corners and even though your transom is straight across, a small amount radius across the back helps.
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Old 01-27-2009, 01:19 PM
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Default Re: Building a Fiberglass swim platform

I am not set on 18 to 20 inches long. I feel the longer the better also but I just want what looks right. I am not to concerned with weight as the boat is a little bow heavy. With the cabin far foward and all the crap I put in that. I could easily go to 3/4 ply and cut out one layer of mat and one layer of 1708 on the bottom. i was thinking of glassing in some stainless nuts for the brackets to bolt to instead of through bolting or 5200 and screws.

I can get the 1708 for about 10.25 a yard by 50 inches so 3 yards gets me two layers if I cut it in half lengthwise. I was worried if I user woven roving I could not make the bend onto the flange
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Old 01-27-2009, 01:49 PM
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Default Re: Building a Fiberglass swim platform

you can buy really, really nice platforms in the $1500-$2000 range, custom made for your boat from someone that has already taken the tiem to make a mold.

If you have more time and skill then money then im all for making your own, if you want to order something that will look like it came with the boat when it was new leave it to the pros.
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Old 01-27-2009, 02:02 PM
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Default Re: Building a Fiberglass swim platform

Quote:
Raybo Marine NY - 1/27/2009 1:49 PM

you can buy really, really nice platforms in the $1500-$2000 range, custom made for your boat from someone that has already taken the tiem to make a mold.

If you have more time and skill then money then im all for making your own, if you want to order something that will look like it came with the boat when it was new leave it to the pros.
Its not the money or leaving it to the pro's. I like doing projects and have worked with fiberglass before. There is no reason I can't get a "professional" looking finished product by doing the work myself.



By the way I am looking at 250 to 350 dollars in materials. My time is free so add that to whatever the brackets cost me and I have a platform for about 1/5 what a professional one goes for.

Plus when someone asks where did you get that swim platform I can say I made it.
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Old 01-27-2009, 02:14 PM
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Default Re: Building a Fiberglass swim platform

You can get good results, all it takes it time and patience.

I look at everything like a job, figure how much your time is worth to you, $20 a hour? $30 a hour? Then figure out how long it will take plus materials.

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Old 01-27-2009, 02:46 PM
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Default Re: Building a Fiberglass swim platform

You might want to reconsider not attaching the actual platform to the boat. Attaching it will give you lateral stability that would be lacking if it's just hanging on brackets. If you bang into a dock or something you could twist the brackets or pull the fasteners.

Building a mold with melamine is no big trick. I think you have the right idea there. I would suggest just one coat of wax and skip the PVA, you don't need it. You could build the radius on the flange with MDF covered with formica. As far as the radius that transitions from the deck to the flange, you can use wax fillets there (1/4" minimum) or just break the edge after you demold. Wax fillets sometimes cause prerelease so be mindful of that if you use them.

Woven roving will lam into the transition okay if there is a small radius. If the corner is square (no radius, break after demold) you can make up a radius compound with milled fibers and resin. Mix it to the consistency of toothpaste and put about a 3/8" bead in the corner before you skin coat and roll the skin into the wet compound with a 3/8 " diameter lamination roller.

As far as laminates, I would opt for a 1.5 oz skin coat, 1.5 oz mat/24 oz woven (x2), 1/2" Divinycell bonded with putty, 1.5 oz mat/24oz woven (x1) and a finish layer of 1.5 oz mat. That should give you a flange thickness of around 3/8". My choice of Divinycell is for rot prevention more than anything else.

Resin usage for mat is about 3.5 oz/sq ft by weight. a combo of mat and woven is about 4.6 oz/sq ft by weight. These measures are for fairly dry laminates. Add 10-20% for wet laminates. Also figure 10% for waste.
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Old 01-28-2009, 02:11 AM
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Default Re: Building a Fiberglass swim platform

jy118lfd, OReely suggested a nice laminate but it probably could still be lightened some (.75mat, .75mat, 18roving, 18roving, 3/4 or 7/8 in 4lb. foam, 1.5mat, 24roving, .75mat. I would also suggest one or two additional layers of mat in the flange before the last roving goes on. I am sure that roving ( particular the light roving I am suggesting) would lay into your mold easier than the DBM, but also the 0/ 90 fiber orientation complements the structure better. Rather than trying to put stainless steel nuts into the glass I would stack up four or five layers of 1708 that vary between two and three inches in width, on the landings of the brackets. If those were laid up nicely they can be finished with a layer of mat and you could drill and tap those to 1/4x 20 machine threats ( people don't understand how well fiberglass can hold threats when the fiberglass is laid up well and cured well).
The text that I use for holding forces ( Gibbs and Cox,inc) shows 3/8 inch of mat and 1/4x20 machines screw as having 600 pounds of axial loading ( in-line pull) and 1900 pounds in sheer. As I said those values are for mat and the laminate I suggest a would be slightly higher in the axial loading at the same in sheer as 1900 pounds is where the fastener shears.
I also agree that molding a flange for mounting has structural benefits ( with an upward turn flange being stronger than the downward turned one) and is not that difficult to do.
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Old 01-28-2009, 04:27 AM
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Default Re: Building a Fiberglass swim platform

I really have no source for divinicell and to try to get a one sheet would cost me an arm and a leg to ship it.

I agree that there are better ways to build it and using the more exotic foams you can build a lighter structure. But using foam for merely rot resitance does not sound cost effective. Properly encapsulated the wood will outlast the boat. Its not going to have holes drilled in the wood when I am done. I am thinking about drilling and tapping threads as was suggested. That sounds like a good idea. I am also going to bond the platform to the brackets with 4200 for additional strength as well as build a flange for the platform to attach to the transom. It will turn down though as I want it to look clean and fitted.
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Old 01-28-2009, 09:26 AM
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Default Re: Building a Fiberglass swim platform

I don't think the D-cell would cost but a few dollars (maybe $20) more than the sheet of marine ply you started out with, even with shipping. If you're going to use plywood for cost savings you might as well use A/C fir. It is the same wood and glue as marine ply at about half the cost. Marine ply has more layers and less repairs/voids and is slightly better on physicals than A/C fir but not enough to worry about, especially on a project such as yours.

A point on construction with plywood - how are you going to assure that you have contact with the glass in the mold when you bond they plywood down? You can trap air between the plywood and the glass. You should drill holes in the plywood in a grid pattern of about 6" x 6" and then weight it down (a lot of weights) while the resin cures. Or you could cut the plywood into 6" x 6" squares and press them into the bonding putty or a real wet layer of mat (no weights needed). Either of these methods will add to your labor (another reason to use D-cell for me).

As long as the wood is sealed (and remains so), you're right, no rot worries. However, any crack or hole is a potential for water ingress, hence my recommendation for D-cell. Where you drill and tap your mounting holes is going to be a possible entry point.

Good luck on the project. Keep us posted.
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