Thread: Transom stiffener for TS16

Typically a stiffener will be little more then a rectangle of plywood, glued to the inside (or outside) face of the transom. This serves as a localized stiffener, offers more "meat" for bolts to pass through or clamps to hold onto.

Generally you'll want to increase the total thickness of the transom in the engine clamp area to 3/4" (18 mm). The larger you make the backer board, the more you'll spread out the strain of the engine on the transom. This size is good to about 8 HP, which is way more engine then a TS-16 can ever use. 5 HP is just fine for this boat and you can find models with reverse gear too, which I find very handy. You could easy get by with 3 HP for most conditions on your TS-16.

Do not over power your boat. It will not go any faster (honest), it will just suck up more fuel, make more noise and pile up a huge wake as the engine attempts to beat the water to a froth with it's prop.

On Sixpence, I put a hardwood, sacrificial board on the outside of the transon, the idea being that the outboard can chop that around and when it gets too gnarly, I can plane it off and fit another.

Pity she's going to be launched as a rowboat

Richard

You've checked the boat plate regulations have you? I'm pretty sure that (in this state), if you register her as a sail boat, you don't need the boat plate. In my case, I started Sixpence before the cut off date so I'm doubly safe.

Richard

I had a wooden stiffener in mine (which I don't have a photo of) but as it had a small bit of rot under it I replaced it with this stainless one when I was cutting out the rot. I still would not trailer it with the outboard attached though:



here it is in place:



The piece of dowell with a hole in it is just to locate an extendable piece of aluminium tube tht I use for my mast crutch when trailering and extend for my boom tent when camping.

Looks a bit rough here when I was setting it up but it works well:

I had a closer look at the plans again today and found it.

It is marked on the plans as a 12" by 3/4" peice of solid timber going across the frame level with the gunwhales.

Use plywood instead of solid timber stock for the transom reinforcement. It's more dimensionally stable, has higher cross grain strength and generally spreads loads better.

16mm ply wood?

It is going to be all covered with and glued to 6mm ply for the transom anyway. I would have thought that would make it plenty strong enough?

16 mm plywood is fine as are two layers of 9 mm. Soild lumber used in engine mount applications are best if in compression, like engine beds under an inboard for example. Solid lumber, unless well encapsulated in epoxy will swell and contract quite a bit with moisture content changes. This eventually leads to loose fasteners. Plywood is much more stable in this regard and spreads loads better too, so it's a natural choice here. It's not a strength issue so much as a durability issue.

It just seems insane to go out and buy a sheet of 16mm ply for such a small job.

Reading between the lines it look as though if i enclose it well in epoxy and add the ply on the transom side then it will be ok to use solid timber?

Originally Posted by hereselmo1

It just seems insane to go out and buy a sheet of 16mm ply for such a small job.

3 layers of 6mm laminated together gives you all you need and there's a good chance you'll be making it out of planking scrap. Similarly for any thicker bits of ply you've got lying around.

Sixpence's transon is two layers of 9mm laminated together ... but with the size of the two bits, that's nearly a full sheet used up.

Richard

Using solid timber between the plywood of the transom and a piece of plywood to cover the pad would be fine too.

Don't you have any 6mm or 9mm ply leftovers? Thought there would be plenty on a TS16.

MIK

I have plenty of ply. I havent even started to cover the hull yet.

To be honest I dint even think of glueing several peices together. Must need some sleep.

Originally Posted by hereselmo1

To be honest I dint even think of glueing several peices together. Must need some sleep.

No, we all overlook the screamingly obvious ... though usually AFTER the deed, not before it, you're actually ahead of the game

Richard

If you elect to make up the reinforcement patch from pieces of 6 mm, then stagger the joints and cant the grain pattern a little, about 12 degrees offset to the one below and/or above it. This is a cheap technique to improve strength, with no additional weight or material. It's also how powerboat transom cores are done too, where strength issues are serious in many cases.

For example on a recent transom core replacement I preformed for a local fellow, his 16' boat had a 125 HP outboard on it. This was the maximum size it could carry and it was part of the reason the core failed. The factory used 2 layers of 3/4" plywood (18 mm), both glued at 12 degrees to their respective centerlines. Standard practice stuff, but not quite good enough at the high end of the horse power scale.

I replaced the transom core with 3 layers of 1/2" (13 mm) each canted at 12 degrees to the next. The transom was still the same thickness, but the original core had 10 veneers of wood in the plywood laminate and one glue line. My revised 3 piece laminate had 15 veneers of wood and an additional epoxy glue line (2 total). It weighed the same and was about 20% stiffer because of the canted pieces and the extra veneers in the laminate. Of course I had to use another full sheet of plywood and had to cut and fit 3 pieces of core instead of two, but this is a fairly small price to pay for the strength gain and probably enough to compensate for the huge engine hanging off it on this boat.