Question for GN7

[WESTERNAERO]

GN7, so with 90% of the work being on the bottom of the prop, Does it really make a difference if the mounting flange on the strut is flush with the bottom of the boat. See strut pic, this is what I have now.

[gn7]

GN7, so with 90% of the work being on the bottom of the prop, Does it really make a difference if the mounting flange on the strut is flush with the bottom of the boat. See strut pic, this is what I have now.

As far as the prop is concerned, it makes no difference. As far as overall hull drag, like anything else under the boat like fins, rudder, water pickups, the entire strut, and even the prop shaft itself, it makes a difference. Putting your index finger in the water at 100mph does not effect the prop, but it effects the speed of the boat.

[WESTERNAERO]

I'm planning on building a new strut, so really I'm just trying to get ideas on which way to go. The hull thickness on the boat is only about 3/4" so I'm thinking a drop thru might be best. If I recess the bottom and do a bolt on like I have, the floor will be too thin I'm thinking. Then I will have to do glass work inside to build it up. The pic below is the main reason for doing a new strut, the whole thing should have been about a 1/2" higher to begin with. Plus I'd like to move up to 1-1/8 dia shaft.

[WESTERNAERO]

So what do you think GN7? Drop thru, bolt on without the recess or bolt on with recess and build up the inside. I not going racing and I'm not trying to rotate the world, I'm just wondering which would be the best option. What you think, Thanks.

[gn7]

Hydrodynamic drag squares with speed. If the thing doesn't hit 80+, and you never expect it to, then I am not sure there is much benefit. If you are considering a 1 1/8 shaft, sounds like some HP is anticipated. Drop thrus are not only more streamlined, but done correctly, its stronger.

[WESTERNAERO]

Funny you say that, The last time I had it out I actually checked the speed on a GPS and we were doing 82 mph @ 4900 RPM with a lot of boat it the water. And that was with 0 boost actually it was -1 on the gauge. So I am concerned about safety as i start swapping pulleys and making more power. Hence the strut and shaft swap this winter along with moving it up a little to stop the shaft from rubbing. So a drop thru should be the plan you think?

[gn7]

Funny you say that, The last time I had it out I actually checked the speed on a GPS and we were doing 82 mph @ 4900 RPM with a lot of boat it the water. And that was with 0 boost actually it was -1 on the gauge. So I am concerned about safety as i start swapping pulleys and making more power. Hence the strut and shaft swap this winter along with moving it up a little to stop the shaft from rubbing. So a drop thru should be the plan you think?

don't get me wrong, the bolt on surface steel strut is more than strong enough for a lake/river boat. I was only saying that the surface mount doesn't make much diff at speeds under 80 or so as far a drag. Your setup will handle more power than you are giving it. There have been GNs pushing more then 1000HP with surface bolted struts and 1 shafts(Aquamet22 or K Monel), they may have given up a little in top speed due to drag, but OK so far as strength.

The biggest issue I have with you current setup is the rusted chrome at the weld. Campbell Carl had a similar strut and the weld failed due to the rust. Its hard to tell exactly how much the strut is effected unless you remove it and strip off the chrome. But the strut itself is pretty stout, like somebody planned to put so power to it.