JEM Watercraft

Sorry mate, the skeg was 5 cm thick and İ tapered it down to 2.5 were the SS strip was attached to save a bit on weight with out losing too much on strength.

This is an incredible build. How thick is the plywood you're using? Will you be able to flip that over without help? I'm anxious to see the interior fit out on her. Good looking build!!
Thanks for posting the pictures.

Lee

Hi Derek,

Thank you for the tip on where to get the stainless strip. I will try the junkyards first. You put just the one skeg on? I am thinking about putting a shorter one one either side of the middle. I will put the skegs on after glassing the entire bottom. I was thinking of a 2.5 cm (1 inch) thick skeg about three inches deep at the stern. I am going to try to get enough stainless strip to cover the bow also.

And the shorter two skegs on either side of the middle will also serve to reinforce the plywood from excessive flexing. Lee, the middle section of the bottom is the only 9mm piece on the hull, the rest of the hull is 6mm. Another builder reported seeing the bottom flex when moving in the water so I want to stop that as much as possible. If the boat were fully glassed I could flip it by myself but I want to cover all the seams inside and out first, then glass the hull and add the gunnels. Then, I think it would be safe and easy enough to flip by myself. I will be making some wheels to help with the launching. I just returned from Samal Island after getting the layout done for the sea wall.

When I post some pictures of the interior after flipping the boat I would appreciate some ideas on how to handle the fitting out.

Dan in Davao

I wonder if a thinner bottom with longitudinal "mini-skegs" would prevent the oil-canning and add the "scrapability" you're seeking, while also saving some weight?
I'm not familiar with your waters, so I'm sure you already thought of those and opted for the thicker ply under foot.
That boat just looks fast!

Lee

Hello Dan, Yes İ put only one skeg on my boat. You are probably familiar with the standard Philipino fishing boat. Long, narrow with bamboo outriggers. Thats what İ had, The good ship Bomshankar. There,s only place for one skeg.
Anything you can do to stiffen the bottom is a good idea and since your planning 1 inch by 3 inch skegs pt & stbd, consider a 3rd down the center line. !.5 inch by 5 inch.
İ,m not a marine architect mate but İ motored and sailed around your area for 5 years and (as you probably know) the sea conditions can turn shocking real quick.

Yes I am familiar with banka design. Here in the south I commonly see a solid log keel with plywood epoxied on for the sides. This boat will not have any outriggers (catig). The locals are leery of any boat without catig.

You used a 1.5 inch wide by 5 inch deep skeg. I was planning on a long central skeg much like yours except I was thinking of 3/4 inch to one inch stock about 3 inches deep. The central skeg running from bow to stern and two other side skegs on the 6 mm plywood to control oil canning and for bottom protection. They would be only an inch or so deep, and laminated to follow the contours of the 6 mm. Are there any specific reasons you recommend the thicker and deeper skeg?

Dan in Davao

After filling all the seams and plugging the wire holes I was able to complete the fibergglassing of the seams this morning. Tomorrow I can turn it over and better see what I have made. Next step is to start glassing the inside seams and bulkheads. She is starting to look pretty sleek.

The holidays and my constructions projects on Samal have wreaked havoc with my building time.

I do love the tropics where epoxy setting temperatures are here every day and never a flake of snow.

Dan in Davao

Stunning!

Lee

Hi Dan, My thinking about a thicker central skeg is purely a mechanics story. The contacting area (base of the skeg to the hull) will be the deciding factor when you get shoved side ways by wave action and meet a rock, just there. Your skeg is the lowest part of the boat, so apart from better tracking when underway, İts the first line of defence in shallow waters. İt gets bashed first. Mechanics thinking says "make it strong".
Thats why my skeg was 5cm thick at the contact and tapered down to 2.5 where the SS strap was. Something else İ did there was to put hand grips in the skeg. İ tend to think about "worst case scenarios" and try to plan and build ahead. İf a banca turns over in rough weather the outriggers will be under water. You cant hang on to them. The boat wont sink but theres nowhere to hang on to except the prop and the little bit of shaft. İn rough weather you will probably need to hang on, so İ put hand grips. 2.5cm by 10cm cut right through and rounded out to be as hydrodynamic as was possible.
As it happened, İ never did capsize but it did give the locals a good laugh so the effort wasnt entirely wasted. Derek.

Thank you Derek for explaining about your skeg width. Good, sound thinking. I will be strengthening my skeg attachment with fiberglass and this may mitigate having a thinner skeg. Esthetics and weight were my primary considerations but you have made some significant points about strength. Thinking about clinging to the smooth bottom of an upturned boat shows the need for some kind of gripping point.

I have conducted some tests on capsizing with my PDRacer and I can see I should do the same with this boat. Dinghys are very stable when floating upside down so I should find out how easy it would be to right it. Needless to say I will do this test without the motor although I should attach a suitable replacement weight. I may want to put handholds in the skeg too. Like you say, keeping the locals entertained but more important, knowing what to do if you capsize.

Dan in Davao