Swim Platform Construction

[CascoBay]

Here's a better look at my overall plan. 5 supports. The 3 middle ones go out 48" so that I can stand my inflatable row boat up on end, 70 lbs. No other weight will extend out that far. There will be a railing limiting travel to 36" out from the transom.



The 2 outside supports extend 36" out and due to the hull bottom, do not have enough room for a larger angle on the support.

 

[jbcurt00]

Thats a lot of leverage

Probably need the angle to come out more then 1/2 way out......

 

[CascoBay]

The 3 center support angles come out 36". The outside supports are a total of 36", support angles are at 16". I may cut the side brackets back to an overall of 30".

 

[Baylinerchuck]

I'm Irish! May be a touch redneck though....

Here's what I'm debating currently. Which option is better?



OR

Definitely the second pic as it spreads forces out evenly across the transom as opposed to concentrating forces in two points.

 

[Baylinerchuck]

On my opinion with 5 gusseted supports tied through the transom with blocking on the inside, it should be plenty solid. I don't think you have anything to worry about.

 

[CascoBay]

Thank you! I've been running this through my mind for months, I tend to overthink things like this.

I've bounced this off some of my colleagues and they tell me gussetting them together is key as the load will be shared.

 

[jbcurt00]

That's the right idea, I would suggest making them out of some thick material and therefore you won't need to go so far down to get the same support. Use plates on the inside to tighten against.



These are a bit on the thin side but still good enough depending on how wide the platform will be.

Notice where the angle support connects to the horizontals in these factory brackets.

And none of those are 36-48in swim platform supports.

Still think the leverage is too much for that angled support to intersect at 16in

A 3in rail to limit travel out from the transom? W another foot sticking out past the rail?

 

[CascoBay]

I can't see your photos but I know where the factory platforms are supported, on their leading edge. They are also not framed in steel, but fiberglass and wood. I am hoping that helps my scenario, but I am not sure.

The railing will be at 36" out. The purpose of the railing (think Ranger tugs swim platform) will be to support the dinghy in a vertical position (think Weaver davit) at the 36" to 48" area of the platform. If I didn't want to carry a dinghy the entire platform would be 36" out from the transom.

Keep in mind only the outside support is short. The 3 main supports are substantial in terms of framing.

 

[gsxrdan]

to add my 2 cents, u dont have to restrict the angle support to 45deg. id like to do a removable swim platform if i can and am curious about leverage issues also. the ultimate support is what Sean_Nos has done, well worth a look.

 

[CascoBay]

I understand. Keep in mind it's only the outside support that is short in support.

 

[alldodge]

Don't see the need for the vertical support the transom. The edge or the upper brace will wear into the hull over time. The bottom point bracket covers the end of the angle but should be wider. The lower attaching point can be small because it has only up and downward forces. The upper attaching bracket should be wider because this is where the most forces are found.

 

[CascoBay]

Good info thank you. I am trying to figure out, if I remove the vertical, how to make a wider pad for the attachment point. It is well above the waterline, will aluminum and stainless work here? I have some 3/4" aluminum stock 8" wide that I can drill and tap but it will be a stainless fastener and angle bracket.

 

[alldodge]

The strut channel your using can be 304 or 316 stainless, and I would not use aluminum with it. You could look for something like trailer bunk brackets in SS or galvanized. If you could find a welding shop an see if they can weld a SS plate on the end of the upper channel. Wide enough to get a bolt on each side and one below.

 

[CascoBay]

Great idea. I would think that having the rear vertical would lower the stress on the top bolt of the bracket alone, because if it flexed outward the additional bolts found in the vertical would spread the load.

 

[alldodge]

Great idea. I would think that having the rear vertical would lower the stress on the top bolt of the bracket alone, because if it flexed outward the additional bolts found in the vertical would spread the load.

It would in the downward force, but then I would suggest using more bolts going down the length of the channel. From my view I see the greatest load on the very top. This is why I would recommend a wider surface area to disperse the load.

Just my thinking, others may vary

 

[CascoBay]

Makes sense. Thank you for the input!

 

[proshadetree]

Totally depending on your deck design and the way they are fastened to the platform length will not play as large a factor as one might think. Depth will. If you have supported your platform and can connect the brakets securely horizontally it is irrelavant. The vertical support spread at the transom is where you will gain stability and strength. You will pull more at the top and push at the bottom but the solid vertical bar will not allow stress points in the hull.

 

[CascoBay]

Here's where I'm at. I want the platform to be on the same plane as the waterline, so I placed a straight piece of wood against the hull to get the proper angle. A bit rough but it should work. I then adjusted the 1 support I had mounted to use as a template.





I also took the above advice and changed the angle of the outside supports so that there wasn't as much cantilevered out.



This weekend I will mount the 2 outside supports and using a straight edge, will determine where the 3 middle supports will land.

You'll note that the platform is going to be roughly 12" above the waterline. Some may think this is excessive but I'd rather give it some free board to lessen the stress from waves.

You will not be able to see any framing when I'm done. I will install side trim that wraps around the sides and rear.

 

[CascoBay]

I made up 4 backing plates. 2 per outside support, 3 on each of the middle supports.