Question for GN7

[WESTERNAERO]

Sorry it took so long for me to answer this. I don't venture to the v drive forum much because it tends to be dead here.
Unforgiven is part right, part wrong. Sorry Ed.

He is 100% dead on about the cracking. If a strut is going to crack or fail, it will start at the front of the strut where it is tapered to a sharp edge. I try to minimize that as much as possible, and as short a taper as possible, but its still pretty damn thin there.

But there is no forward thrust at all in the strut, and 99% of the forces it sees is upward and pretty even across the length of strut barrel. A little bit more towards the rear due to the prop being on that end, but its pretty even across the strut barrel. The wear of the bushing shows the forces, and they are almost entirely at the upper part of the bushing because the prop is trying to lift the ass end of the boat. On a hydro its entirely on the top side and virtually none anywhere else.
As to why the outdrives are tapered on the back side, and the V drives aren't, its kind of a physics thing, and a damn good thing it works out like this, or outdrives wouldn't work worth a shit.
Look at the bulk of the outdrive above the prop center line. Now compare that to the bulk of the strut above the centerline. Now look at the bulk under the prop centerline of both. Which has the most bulk in front of the prop in each case. The v drive nearly nothing above compared to the outdrive, and zero under the centerline.
The below centerline is where 90% of the work is being done on both cases. Look at a hydro. The prop is half out of the water. Same with a Ilmor, and Merc Nighthawk surface drives and in the right conditions on the right hull, a #6 and 8 Merc, and some Imcos. AND THEY HAUL ASS! At any given point in the prop rotation, the downward ear, to the mid rotation point, is doing much more work that the upward ear(s). Its the downward push that lifts the ass end, on any boat, specially a hydro. If the upward ear did the same work, they would cancel each other, and hydros wouldn't lift, and surface drives would be stuck in the water.
Another reason the bulk above the prop on a V drive means so little and has a little more effect on the outdrives is the number of blades. On a v drive the blade at the top is doing near nothing except thowing water off the perimeter of the blade into the bottom of the boat. It lends very little to the forward motion of the boat. Again, look at hydros. NO blade in the water ot the top at all. Look at the speeds of hydros and surface drives, they don't miss that balde out of the water one bit.
If the upper blade did much, the outdrive would suffer much more than the skinny ass liitle blade the strut has.
So the fact is, the tapered on both ends skeg of the outdrive is effecting the prop more than the blunt back side of the strut on a v drive, because its under the prop centerline where the prop is doing the majority of it forward thrust.
Make sense?

Yes this makes sense, thank you very much.

[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.

[WESTERNAERO]

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.

Thanks for your time and opinions GN, I do appreciate it. Hope I'm not bothering you with this on this site, I know you spend most of your time on PB. I would like to get the V-drive area here up to speed here though.
This boat was original rigged by Dimarco with a blown BBC. It probably explains why this boat is setup originally with the strut angle and position very close to what other guys are changing to with their Howards and Spectras. I'm with you on the chrome, it makes me nervous not knowing whats under there. Just one more reason I'm planning on changing it.

[gn7]

That thing looks like it was built to take some power. Didn't mean to make too much of the strut, just a heads up that the chrome can hide some stuff. I seriously doubt it would ever fail catastrophically. Just keep an eye out for cracks that night appear in the weld area until get around to replacing it.
Odd that your shaft hole is off like that. Not sure the strut was suppose to have a shorter web, as much as I think somebody oopsied a little when they done cut it. They are usually with the strut in place, and a shaft run thru the strut with a hole saw on the end. If they don't watch what they are doing, the hole saw can walk down the hull a little before it bites in and starts cutting.

As for PB, that place is a spin off of the original HB, and the V drive guys were the first ones to make the move when HB was flaming out. The V drive forums there still get the majority of the posts. Each site kind of takes a direction from the start and heads in a general direction. Not sure why, but the V drive forums there are kind of petering out. Jet and dyno forums are still holding their own pretty well. But the V drive forum has taken a dip lately.
Still WAY more boating content at PB and here than there is at RDP. That place is 100% lounge, and by invitation only. No party crashers allowed unless you sit down and shut up. They will let you know when its your turn to speak, and what to say, and to who. Place is foocked up.