Glen l tug a long

Would like to add a 8” x 24” x 12’ box keel to a 16’ tug a long hull. I would like to have the water drain into a section of it below the sole in the cockpit and have a bilge pump so when left in the rain, water does no5 fill the hull. The front section I would divide into a few sections so I have positive buoyancy boxes built in. I would like to make it unsinkable. Would adding the box keel negatively effect the hull in any adverse way. I am not super familiar with boat terminology, so I hope I am describing what I am trying to do correctly.
My CANDU EZ I leave uncovered during a lot of the summer and when it rains it fills with water I have to bail out.

 

If the sole is above the hull bottom, why not build a bilge pump well?

same for pos buoyancy, add foam below sole?

 

It is a stitch and glue plywood boat with flat bottom, so the sole is the plywood bottom. That is why I want to add the box keel below, so I can have a bilge. I was going to make some enclosed boxes under the berths for buoyancy ,but it takes up storage space.

 

Any picture of the hull?

 

Tug Along Design - Boatbuilders Site on Glen-L.com https://boatbuilders.glen-l.com/tug-along-design/nggallery/tug-along-design/tug-along-by-glen-burston-london-ontario-canada

Cute boat.

As long as the new box keel doesn't contribute too much to floatation, you could probably make it work. If the keel lifts the boat in the water any, you may introduce more rolling in the hull as the chines contribute less initial floatation. The heel angle would have to increase for the same righting force to effect her. It would be almost like balancing her on her keel.

You might also consider a grate to lift your feet above the pump intake.

 

I think you can do it. The shape in the front should be faired in, so the size at the beginning is zero. There is no way I'd go 24" wide. I'd go more like 10-12" wide.

The box needs to be glassed to the hull exterior, so you have to remove all paint or you'll be tabbing to paint which will break off.

And the sides of the box need to be strong enough and wide enough so if you ground; they don't shear the hull or crack it.

Consider using 3/4" plywood sides or building a pad for the hull with 3/4" ply. The pad would be somethi g like 2" wide with 45 degree sides 3/4", then the edges of the box sit on the pad so if the boat ever rests on the box keel; it won't break the hull.

Then for the box keel itself, similar, probably on the order of 3/4" plywod because if the boat ever teeters on a rock, anything smaller will crack.

You won't need to worry about r.m. unless you build it poorly and too large.

Personally, I'd build a pump well. Same concept as what you have planned, but smaller and to the back. The flotation foam doesn't really belong in the bottom anyway.

 

I should mention that the hull is made of 1/2" marine ply instead of the 3/8" ply called for in the plans, so the hull is heavier then called for. I purchased the hull from someone and it is a little overbuilt. If the hull is too buoyant with the box keel, could I add ballast to make it more stable?

 

The hull is not completed yet. It is upside down on trailer and I am getting ready to rout corners and glass seams. So if am going to do anything now is the time. I was going to build it strong like you suggested so I will not have to worry about beaching or hitting rocks.
I will try to get some pictures posted. I like my idea as long as it is not going to effect stability.

 

Yes, but I honestly don't see it being a problem. You just want enough volume to accommodate the bilge pump intake. I doubt that will have a significant effect. I was only talking through the dynamics of providing additional floatation under the water in the center because you had mentioned wanting to add flotation to make her unsinkable. I know you weren't describing the flotation as part of the keel. I was just cautioning against doing so. Many small boats with built-in floatation add the floatation high up so the boat won't turn turtle if it fills with water.

 

It is not going to become too buoyant if done right.


That means more like 1/2" high by 10" wide at the front and 8" high by 10" wide at the back or aft, and the foam is used elsewhere.

The displacement of tbe above at 12' long is like 200 pounds only; the 3/4" plywood and glass is like 60 pounds of it. If you can find more appropriate homes for the foam (keel is not), let's say you want 1200 pounds of buoyancy?, that is about 20cuft of foam or 40 pounds, so you are adding only 100 pounds of displacement or so..

Conversely, a 2' wide box by 12" deep by 12' long is 24 cuft or about 1200+ pounds added and the boat would get weird indeed.

 

8" x 24" x 12ft is 16cubic ft, that much buoyancy will make your boat fall over! It will displace 64lb. per cubic ft.

1 Put a cover over the cockpit.
or
2 Arrange shallow bilge pump pick up at the forward end of the cockpit where it is lowest (according to drawing supplied by Will).
or
3 If you make a small sump (min. required for pick up) make sure it is protected from grounding.

 

This is a wood boat. There is no way you need that much flotation foam on a 16 foot boat. But you do need to put it up higher on the sides where it will be effective if the boat should swamp. And it needs to be distributed so that the cabin doesn't make the boat roll over. That's an outboard so it needs level flotation. It being a Glen L design they must have given instructions on how to install flotation. Or see my page on how to calculate how much flotation you need. Boat Building Regulations | Level Flotation https://newboatbuilders.com/pages/flot2.html