Tips for making a custom fiberglass swim platform?

[thormx11]

So I would like to add a swim platform to my boat over the winter. Most places want over $2k (which I am sure is worth it) but I do not have the funds to pay for it. Nobody offers a platform for my boat, and would need me to take all the measurements for them to make one anyway, so I figure I could do it myself with the measurements. I have worked with wood/fiberglass many times, so I am not too worried about that part.

The boat is a 1995 Century Arabian 24. The built-in swim platform is only 17 1/2'' wide, and when when we tie up to our regulars on the lake it is a large step from our boat to theirs. I would like to add about 24'' from the center of the current platform, which would add roughly 29'' on each side, if I make it a straight edge across the back. I would make it lay over the current platform, and extend out an extra 24'' from the center.

I would probably use 3/8'' plywood (maybe treated?) as the base and then use something underneath, like 2x4s to form a frame/edge for the part that extends off the boat. The I would add a few layers of fiberglass, sand it smooth and gelcoat it afterwards. Currently my ladder just folds/flips up on top of the swim platform and I would like to add a ladder (4 step if possible) that stores under the new swim platform so it is out of the way when not in use.

As for bracing, that is where it gets tricky (for me anyway.) I could add two straight braces from the swim platform to the transom towards the center, away from the outdrive. But I am not sure how I would brace the side edges. I am not sure what they are called, but my boat has 2 compartments in the rear that stick out form the transom, thats where my batteries are installed. I don't think I would be able to run a straight brace from the swim platform to the transom itself. I could maybe run the braces from the platform to these 2 compartments though.

When it is all finished I would probably add something like Seadek to it.

I have searched online and haven't really found much info on doing something like this. Except for one other guy on this forum but he is working on a larger scale (and budget!) than I could do.

 

[Scott Danforth]

Read Teds thread https://forums.iboats.com/forum/boa...1739-custom-fiberglass-extended-swim-platform

 

[harringtondav]

Structure will be critical. And I wouldn't rely on the OEM platform for providing more than it's design intent. Your goal of extending a platform 29" from the transom involves considerable loads. If you build it, many people will stand on it. Take a low ave of 150# per person X the max that could be on it. 600-900#.

My pal replaced the factory platform on his 42' Bluewater. He used the four original transom strut and joist anchor pairs, and built aluminum channel horiz. joists with an alum channel beam welded at the end of the joists. He used 3/4 solid alum bar as the new extended struts. Then capped it with a plastic 2 x 4 or 6" decking product, shaped at the transom for it's curvature. Straight boards after that. His new platform is about 36" deep. He's thinking about adding an extra center strut. Beefy family.

You will need a similar angled strut structure to support it. Meaning you'll have to anchor these struts to your transom - somewhere solid. Forget wood, unless you want to rebuild it frequently. If your platform is sheet molded, with an open outside edge, you could notch it for your new joists, and keep the extension at the same level.

 

[tpenfield]

Interesting endeavor, which I can relate to.

I would not use wood, because it will absorb moisture and tend to crack the fiberglass. You will be re-doing it after about 5 years.

I'd also give the stern edge a bit of a curve, keeping it 24" from the current stern edge. It will look better.

Your options are (1) to make something that will attach on top of the current platform spanning the width of the current platform area between the side 'pylons' or (2) to attach something to the underside of the existing platform the extends out the 24" beyond the current platform. The available width underneath looks a lot less, but you could make something that extends to the desired width.

Here is a sketch of the options I am suggesting . . .


If you went with a fiberglass and foam platform, you could make the flat mold out of wood, then use stainless steel supports underneath as shown to handle the load. I would figure on about 3/8" thick fiberglass and the edges that extend out could have a right angle to provide for stiff rim and a place to attach the rubrail.

Swim ladder can go underneath. You will want to check the outdrive clearance, etc. for the ladder and the supports.

As far as material. If you use polyester resin, then you will want urethane foam for the stiffeners underneath and around the edges, If you use epoxy resin, then styrene foam will be OK.

There is a link in my thread to yet another forum thread about a guy who made a fiberglass platform out of a wood mold.

 

[kcassells]

You go Ted! That is going to be 1 nice pc. hanging off the back.

 

[thormx11]

Interesting endeavor, which I can relate to.

I would not use wood, because it will absorb moisture and tend to crack the fiberglass. You will be re-doing it after about 5 years.

I'd also give the stern edge a bit of a curve, keeping it 24" from the current stern edge. It will look better.

Your options are (1) to make something that will attach on top of the current platform spanning the width of the current platform area between the side 'pylons' or (2) to attach something to the underside of the existing platform the extends out the 24" beyond the current platform. The available width underneath looks a lot less, but you could make something that extends to the desired width.

Here is a sketch of the options I am suggesting . . .


If you went with a fiberglass and foam platform, you could make the flat mold out of wood, then use stainless steel supports underneath as shown to handle the load. I would figure on about 3/8" thick fiberglass and the edges that extend out could have a right angle to provide for stiff rim and a place to attach the rubrail.

Swim ladder can go underneath. You will want to check the outdrive clearance, etc. for the ladder and the supports.

As far as material. If you use polyester resin, then you will want urethane foam for the stiffeners underneath and around the edges, If you use epoxy resin, then styrene foam will be OK.

There is a link in my thread to yet another forum thread about a guy who made a fiberglass platform out of a wood mold.

The link you mentioned is almost exactly for the look I am going for. Except I am planning to attach the new platform over the current platform, then extend out another 24''. I would bolt through the current platform, then add stainless steel tubes from the new platform to the transom. I just skimmed through the posts for now looking at the pics, I will read up on them more after work today.

 

[thormx11]

Here a a rough picture I made up in paint of what I have pictured, hopefully the finished product would look a little better!

Would wood be a bad idea even if it was completely sealed in fiberglass? I think it would be fairly easy to cut out a piece of wood and build a rim around the bottom edge and then glass over everything and then paint it.

I'm also not worried about the finished product lasting 10 years, a season or two would be fine with me until I could afford a professional platform, if I even have the boat that long.

 

[tpenfield]

Here a a rough picture I made up in paint of what I have pictured, hopefully the finished product would look a little better!

Would wood be a bad idea even if it was completely sealed in fiberglass? I think it would be fairly easy to cut out a piece of wood and build a rim around the bottom edge and then glass over everything and then paint it.

I'm also not worried about the finished product lasting 10 years, a season or two would be fine with me until I could afford a professional platform, if I even have the boat that long.

The wood will absorb moisture through the fiberglass, since a swim platform is subject to lots of water exposure. So, eventually (maybe 3-5 years) you will probably start seeing some cracking as the wood expands, and it will be a downhill slide from there.

 

[thormx11]

Maybe something else could be used in place of the wood? I just feel like something solid in the center would help add support around the edges especially. Maybe a use something like aluminum in place of the wood? Not sure if fiberglass would stick to it though.

 

[tpenfield]

The strength will come from the glass around the outside of the core material. Often foam or end grain balsa wood is used as the core.

 

[tpenfield]

If your time horizon is only a few years, then wood may suffice. It may be a matter if the platform impacts your ability to sell the boat, if it is showing signs of cracking, etc.

 

[thormx11]

Maybe I should just wait a while and try to learn a little bit more about making/using a mold/plug and go that route. I think the extra work would be worth it in the end. I think yours will be a very nice product when finished and my idea may work for a while, but would be nowhere near the quality as one like yours. I will be following along with your build and taking pointers! haha

 

[thormx11]

Or better yet, save up a little bit over winter and pay the professional. Swimplatforms.com says they can make one for my boat for $1345. That'll include include an extra-long 3 step ladder, a non-skid top surface, oval drain port(s), a heavy rubber trim molding, stainless steel mounting hardware and installation guidelines.

 

[fishrdan]

Would wood be a bad idea even if it was completely sealed in fiberglass?

I made my swim platform out of dougfir plywood sealed in epoxy and fiberglass. It's not a huge platform 5'x2', 3 layers of 1/2" 5-ply, then several layers of fiberglass/epoxy. Painted to match the boat, and it's been rock solid for 4-5 years. I used T-nuts for attachment points and paid extra attention to make sure they were 100% sealed against moisture.

I wouldn't use my combination (3x1/2" 5-ply) as it would be really heavy for your size of platform, but the wood sealed in epoxy works well. And, you would most likely be better off doing something like Ted to match your glass boat. My platform is on a tinney, with brackets that could hold the world championship bratwurst eating team.