LB26

[fallguy1000]

What you have drawn could work. You calculate the shear of each bolt at the nut. But the failure here might be impossible to repair. What if the studs bend? Then they cannot be repaired. So, consider repair Les! Same as the integral version. You need to consider what happens if it breaks when you build a boat. It being anything.

The bow pulpit or cleatd are not different. If you don't put backing plate behind it; the damn thing might shear out in heavy seas at anchor or on the dock! Not trying to suggest you use a backing plate here! But you ought to learn to do some calcs as a boat builder. A 1/4" bolt is stronger than the surrounding foam, so the boat wpuld break instead of the cleat...not desirable. If you put a large enough backing plate in; one single cleat may be enough to hold the boat..or the bolts may shear instead of the boat tearing out..see?

A 1/4" bolt 316ss with shear rating of 50% of tensile pf 70,000 psi is 35,000 psi. Many use 50,000 here. I am erring low. Sorry not in metric.

1/4" bolt area is about minor area of 0.0269"" at 35000#/"" is 941 pounds to shear(seems high). So, from a design perspective, a bunch of these would be rather strong...maybe too strong.

I may or maynot seem helpful, but consider how things break when you design and build which is part of building a boat; despite our wishes for the designers to do it all for us.

[fallguy1000]

Here you would not need a bushing, but a hardpoint of 'm200 or coosa 20# or higher (blue).

No bolts, just screws bedded in 3m 4200.

Get a rough design done and order the brackets before you build.

[les2021]

Evening

Point taken.

The outer brackets would only be long enough to have 2 fixings into the transom so my thoughts are bolts through hull with a backing plate would seem the better option as your suggestion.
So in summary I will have 2 bolts in the two outer brackets and 3 bolts in the centre bracket, 7 bolts in total. Bolt diameter is the question....

Cheers

Les

[fallguy1000]

Evening

Point taken.

The outer brackets would only be long enough to have 2 fixings into the transom so my thoughts are bolts through hull with a backing plate would seem the better option as your suggestion.
So in summary I will have 2 bolts in the two outer brackets and 3 bolts in the centre bracket, 7 bolts in total. Bolt diameter is the question....

Cheers

Les

Access will be key. In a foam build, we typically cleat with foam for locker bases and sole.

So, where will such bolts be located? They would be really low and hard to access Les.

Give Mertens some time to reply.

I am not a fan of the method with a backing plate. Access will be nearly impossible.

The backing plate was only an example of needing to do minimal engineering as an amateur builder. Sorry if I confused you.

Nevertheless, the dialogue is good because thinking it through now is best.

[fallguy1000]

The better way to build it with metal bracketing is to screw the brackets into solid frp pads. No holes in transom. Screw are failure points; easily repairable.

Please give Jacques some time to reply.

[jacquesmm]

At this point, access should still be easy.
You should fabricate the swim platform and drill pilot holes for the holes. Or, at least make a template for those holes.
Then, refer to my "foam sandwich notes" and install HD inserts or make single skin backing plates. I prefer inserts.
If you think you will not have sufficient access later, when the boat is complete, use the technique I describe for consoles fastening:
https://boatbuildercentral.com/support- ... lation.pdf
See the one with threated bolts. At the bolts, you weld a thick Al plate to the transom, on the inside and tap that plate for your bolts. You can then bolt and unbolt the platform from outside, no need for nuts or backing plates.
You choose bolts diameters: small ones if you want the platform to break away in a collision, bigger if you don't.

[les2021]

Morning All

Many Thanks Jacques / Dan

I think I am now as ok as I can be on this one.

I now have options so it will be my choice, all input has been very useful so many thanks.

Attached is YES another sketch of my taking on Jacques proposal.

Cheers

Les

[fallguy1000]

Get the brackets measured up and made and that will really settle your nerves and help you decide how you want to build it.

I think you can either make the al insert or lay solid frp on. The al insert might be faster if you can run to an al shop. The solid frp will take you a few days to fabricate, sand, fair, etc,

in the ocean, the aluminum is subject to corrosion, so it should be painted with epoxy primer AND UV TOPCOAT and bolts should be bedded in 4200 to seal the galvanic intersection and reduce galvanics.

Modern adhesives should not be discounted either. Bedding ss brackets in 5200 and ss screws in 4200 into solid frp will not corrode or fall off at sea if you demand 316 hardware. 304 will make you sad..

[jacquesmm]

That looks fine and I second Fallguys note about Al treatment. We have a detailed description of such a treatment in our repair section, Seacraft 23 section, look for the Al bracket description. Some of the picture links are broken but we are working on it.

[fallguy1000]

Here is a guide for hole repair. The 1/4" or 6mm dimension is a bit short for my liking. 3/8" minimum for me...solid frp is made from 600/225 tapes which are about 0.050" per layer, so for 0.4"; you need to wetout 8 tapes; wet them on top of each other and use peelply on the final layer..

See the 1100 pound control? That would be what you get with solid glass and epoxy.

Ps, for hole repairs, the best way is to thread a new hole and then insert raw epoxy and then fill with epoxy and milled fiber and cabosil; then it cannot pull out