Sea Sled madness. It’s in my brain.

Sharp is the key. Less drag.

The bottom chine? Like the port and starboard keels?

Keels are keels, chines are not keels....

The chines where she runs underway create drag if they are rounded. I don’t well understand the hydrodynamics of it because in my pea brain, a radiused corner is less surface than a sharp angle, but I believe the general idea is to release cleanly on the flat versus along a radius. And despite my boat running in the water and not planing, I opted to sharpen the aft edges as well. My boat is suffering from some issues back there (too much rocker and a bit too deep) and I am going to try and work on it this summer, but I digress.

The other thing about the radius versus the flat is that the flatter surface is wider on the water. While it may not be much at say 1/4 to 3/8”; it is a bit.

Perhaps the real story is about turbulence on the radius and the round edge has more. I have a feeling @baeckmo can explain it better, or you can accept it as fact as I did. I never did find an easy way to square it off; just took a few iterations is all.

fallguy said:

Perhaps the real story is about turbulence on the radius and the round edge has more

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I believe that it is due to the Coanda Effect that reduces pressure on the radius. Less pressure along the chine radius, requires then additional lift from the rest of the hull to offset this loss of lift.
Therefore the boat would have to run SLIGHTLY lower in the water to find this additional lift and hence cause more dynamic drag.

Fascinating stuff! Fluid Dynamics is intrinsically interesting even without boats.

If it isn't one damn thing after another. I lowered the outboard to work on the back deck. Now it won't go up. It will still try to go down. Up switch does nothing. Simple I thought. Check the connection at the pump. Nope. The pump is inside the mount. Easily accessible while up. Not accessible down. Huh.

DogCavalry said:

Fascinating stuff! Fluid Dynamics is intrinsically interesting even without boats.

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I like the practical application of Fluid Dynamics, especially when applied to boats which help to make it more understandable, and also the practical application of drinking from a pint mug.
I could never get my head around the theoretical side of Fluids at college many moons ago (ie 40) - I still have bad dreams about momentum integrals.

DogCavalry said:

If it isn't one damn thing after another. I lowered the outboard to work on the back deck. Now it won't go up. It will still try to go down. Up switch does nothing. Simple I thought. Check the connection at the pump. Nope. The pump is inside the mount. Easily accessible while up. Not accessible down. Huh.

Click to expand...

I’d start by making sure you have voltage high enough, then find the switch and see if you get ~any~ voltage up. Salt is hard on everything, I’m learning.

DogCavalry said:

If it isn't one damn thing after another. I lowered the outboard to work on the back deck. Now it won't go up. It will still try to go down. Up switch does nothing. Simple I thought. Check the connection at the pump. Nope. The pump is inside the mount. Easily accessible while up. Not accessible down. Huh.

Click to expand...

You're going to have to remove the engine anyway to build up the cracked transom, perhaps you can make some headway with the hydraulics then.
Of course it could be the switch or simply a wiring issue. Much more likely given it still responds to "down".
Do you have a second switch on the motor itself or just the one on the helm throttle/gear lever?

Wiring I guess. Yes, a switch on the engine. Same response, so a failure between there and the pump.

There should be a pressure relief valve somewhere on the trim unit that shortcuts the two sides of the trim cylinder, so that the engine position can be set manually. It normally has a slotted head accessible from the side of the unit, which can be turned with a wide screwdriver.

To the sharp chines; there are two phenomena at play there.

A/ The fluid relative motion is moving out-up from the keel. A rounded edge allows the flow to continue climbing up along the hull side, causing an increased wetted surface.
B/ Any dynamic lift is the result of a change in the fluid's vertical velocity composant. Thus, the chine should deflect the upwards velocity to the horizontal plane. To do that, there has to be a horizontal surface directing the flow, AND a sharp edge that promotes a clean separation to avoid re-attachement and side-wetting. The chine longitudinal trim angle should be about 4 degrees, as that gives the maximum lift/drag ratio for a flat surface.

Thanks Bodo. I see the valve, and I have a screwdriver here in the boatyard.

I understand what you mean about side-wetting etc. I will add it to the agenda. That area is now painted with 2 coats of Micron CSC-CA, but what has been done can always be undone.

Fairing for appearance. Boss said to.

That is a lot of trowel work, with a badly sprained wrist. But it is almost paintable, before sanding. Going up North for a couple weeks tomorrow at dark oclock. Sanding when I get back.