Building my own swim platform

[Acadia]

Hi,

Posted this on other forums also.....

I am slowly designing a fold down swim platform for my 85 Hunter 40 that I will probably build this winter. I think I have my design put together but always looking to refine it. The picture I attached is what I have in mind with the exception that it will be external and made from wood. For the steps going up, still deciding on those. I have the room inside the hull to cut steps into the back, but not sure I want to get that involved.

Does anyone here have a fold down swim platform willing to share pics and design features?

Platform height -- For those who have or have used a platform, folding or not, how high from water level is it? Given that my design will be folding, it could probably be lower but either way I will build it above the squat line under power. I'm thinking around the 12" mark. Our sailing is mostly coastal cruising.

Stainless steel -- The Hinge will be made of 4" 1/4" Stainless angle. I am thinking of going with 316. Is there any reason I should go with 304? Price diff is not much.

Steps-- This is where the bad drawing comes into play. The drawing is supposed to give you a visual of what I am about to describe, hopefully not more confusing. I will only finalize the step design once I have installed the platform. At the very least I could use the small bolted on steps that are on the boat now. But we would like something more comfortable to climb. So the idea is to build steps that would partially extend outside and inside relative to the hull surface. There would be two rectangular inserts glassed in. Combined with the outer portion of the step, the insert would allow us to have the majority of our foot in contact with the step while climbing aboard.

I was thinking of glassing in additional vertical supports on either side of the stairs (refer to bad drawing). But I'm wondering if it's overkill given that the inserts will have both a vertical and horizontal component perpendicular to the once mostly flat hull.

I would appreciate any input that might improve my design or point out any potential flaws. Not going to start this for a few months so got lots of time to fine tune it.


Thanks!!

[hotdogs]

That picture looks really sharp. I hope that when you complete this project that you will share some pictures of your own boat.

After looking over your design, here are a few of my thoughts:

1) The glassed in supports do not appear to extend vertically to where the wire from the edge of the platform meets the transom of your boat. I would imagine that this would be a point with fairly high loading, so some additional reinforcement may be in order here.

2) What holds the platform in place when folded up? In rough seas, I can imagine it flopping around a bit in ways that you might not want.

3) You may want to angle the steps slightly to ensure that water does not pool in them.

4) Also it appears that in the photograph, but not in your design, the platform swings up to provide a cover over the steps. If the steps are uncovered, I can imagine small birds making a nest here.

5) Last, there are no dimensions in the drawing. Have you come up with some preliminary numbers for things such as tread width, spacing between steps, the height of the platform above the water, etc? These dimensions will greatly shape how usable your actual platform is. As an example, it can be quite difficult for a person to pull their entire weight out of the water and up onto a platform, so you don't want to make it any harder than it has to be.

I hope you find some of the above useful. I'm looking forward to hearing more about what you do with this. Good luck!

[Acadia]

Thanks Hot dog,

The drawing is just a very quick drawing to try and give a better picture of what I had in mind. There are lot's of details missing for example, there will be backing plates and lots of glassing at both the hinge points as well as where the wire meets the transom.

2) There will be a locking mechanism, but I'll figure that one out when I have the platform installed.

3) Good Idea! Adding a very minor slope so water does not get pooled, but not too much to create a hazard.

4) My platform will be external and wood. It will cover the steps partially. But not completely. I would like to make it look like the picture but I don't think I have enough room behind the transom. Luckily my boat is in my back yard and my dog won't let a bird get near the boat .

5)No measurements yet. It all depends on how low I decide to install the platform. I don't want the platform to stick out from the sides when folded but I do want to make it as wide as possible so possibly 2 people could stand on it. If you look at the picture there is a recessed ladder. That will actually flip out and into the water to be able to climb onto the platform. As I am planning a slightly wider platform, I will locate the ladder more to one side so we can use the wire holding the platform as an aid to get out of the water (maybe)

Still a few months away but I will post pictures when I begin.

Thanks

[sailingdog]

First, don't use 304, especially if you're on salt water. You should use 316L stainless steel. 304 has a nasty habit of developing chloride ion stress cracks and failing unexpectedly.

Second, I would avoid cutting into the hull if you can. The transom on most boats is load bearing and cutting several large openings into it without a good idea of what it will do to the loads that the transom has to take is a really bad idea. If you must cut into it, making the openings heavily reinforced to carry the load around the cut areas is a really good idea.

Third, if you're going to make this, make the platform out of foam-cored fiberglass. It will be stronger and lighter than one made of wood. It will also be lower maintenance. Make the areas that the hardware go through the platform solid glass.

Fourth, it would be ideal if the platform would fit flush with the hull when it is closed. That would be the most visually appealing, but probably difficult to do. Having some way of securing it, so that it doesn't open is a good idea, but you should consider making it possible to open it from the water, since your boat is probably really difficult to board from the water without it. If you fell overboard while at anchor, getting back aboard without being able to deploy the platform might be really, really difficult.

Fifth, engineer the hinge very carefully. You're giving it a pretty long lever arm, so it must be able to take the forces involved without failing or damaging the boat in any way. The loads on that platform will be very high...think of the stupid people who will jump down onto it from the cockpit...and yes, that will happen.