Choosing foam core thickness for 3.6 meter power boat

Hello everybody,

I'm going to build a 3.65 meter runabout boat like the photo I've attached, and I want to build it by foam sandwich method. Can you advice me the thickness of PVC foam and how many layers of fiberglass should I use outside the foam?

Thanks a lot

PS: The photo is just for explaining what kind of boat I'm building. When I come back home, I will post the photos of the boat I've built

 

So you don't have plans and building instructions ? There is a lot to consider beside the foam thickness and lay-up schedule.

 

If you want to keep it simple and effective please have a look at the posts of "sailhand". He has a lot of experience with 12ft tenders: http://www.boatdesign.net/forums/multihulls/catamaran-tender-replace-rib-50834-3.html

https://www.youtube.com/watch?v=xFHgh-Xhe2k







Weight is about 45 kg

 

Doesn't seem to be a similar boat to what he has in mind, Manfred !

 

You need plans. Look at Glen-L they have several models that look like your picture.
You can find someone capable to convert specs to composite instead of wood. You
will have to build a complete mold which is just like another boat.

 

Thank you for your replies.

I'm design the boat myself in plywood and It performs quite well in closed water. Now the customers want something lighter so that two people can carry it easily by hands. The problem is that I'm only have experience in plywood not in foam core.

 

This is the plug I build to prepare for the mold. After finishing the mold, this plug will be used as the big flower pot in a marina.

 

What is going to power it ? It will be hard for two people to carry a 3.6 metre boat very far, so I suppose the weight has to be quite low, the total thickness of glass will have to be kept quite thin, I would guess around 3mm. You should choose a foam that has small pores.

 

Gerr's scantlings rules in The Elements of Boat Strength will give you conservative, and therefore somewhat heavy but strong, working values. Someone you know among folks building boats in your area may already have this book if you don't want to buy it.

 

Thanks for your advice!

 

It will be powered by a 15 HP outboard motor. The real boat will be cut at the transom to give space to the motor.

 

I used 1/2 in corecell foam for my 22' flats skiff powered by a 115 hp outboard. 48oz of 45/45 and 0/90. It's holding up well, not a fast boat, but I drive her with confidence at 30 knots. On such a small boat I can't see too much weight savings over stitch and glue type construction.