Shafts thru the transom?

[tom kane]

I hope the thread starter, Buck get his chance to have his say.
I have had a fair go.There is plenty I could add but it would not be appropriate to mention them in public.I would like to watch with interest.tom kane.

[Willallison]

Really? How? My knowledge of props is limted, but surely it is the blade shape that makes a s/piercing prop inefficient whilst submerged - changing gears can't change that. It will stop the normally high-pitch s/p prop from overloading the engine however.

[dougfrolich]

By adding a vent close to the blade when it at the top of its rotation. On the drive I posted a couple of pages back the vent is in the aft portion of the strut, There are many variations on this theme, they work very well. Induced air allows the blade to operate effectivly until the vessel is up to speed.

[Willallison]

Ah - yes of course - don't know why I didn't think of that. But in terms of efficiency, it will still lose out to a conventional prop until it 'gets up to speed' surely......ie approx 40k +

[gonzo]

Can you point out a propeller design that does that?

[Willallison]

Can you point out a propeller design that does that?

Who...me? not sure if you're referring to me or Dougfrolich, Gonzo, but if me - then no - I agree with you.
However, I have seen a number of s/piercing set-ups that use induced air (usually the exhaust) to help the prop spin up to speed. But in my experience (limited I admit) the system is extraordinarily inefficient until the boat gets away and builds up speed.

[CaptPPan]

Have'nt checked the thread in a while... Gonzo here's your shot from the rear. She does'nt throw as much water as an Arnson because the prop is somewhat hidden under the notched transom. By the way, I just picked up a Rolla and should have it next week, I can't wait to see what it will do for my top end. I'm way underproped now.

[dougfrolich]

Great Shot! Keep us posted with the results with the new prop.

[dougfrolich]

ZF one of my favorites

[dougfrolich]

This one is really cool. All these systems with a 2-speed trans and the proper diameter will work very well at under 40 kts.

[Corpus Skipper]

What sort of 2 speed tranny do they use? Often wondered if that was feasible

[Willallison]

Well, now funny you should post a pic of the Q-spd. I spoke to the wife that runs the company and she did say that they ran their boat right thru the speed range efficiently....so maybe you are right after all. On the other hand , it may have just been sales speak - and Gonzo and I are right....

[Buck]

I'm just sitting back soaking in the information and thourghly enjoying the discussion. It seems that there are people making progress with the concept. I am not qualified to add to the discusion but I appreciate all of your thoughts. I'm learning a lot. Thanks (PS) I've got a really, really crazy idea about rudders. Maybe I'll start a new thread and see what you guys think. Thanks again
Buck

[gonzo]

What do you mean by "work very well under 40 knots?". What are you comparing them to? Is there any data?

[dougfrolich]

We put a custom drive similar to the ZF example on a 33' 20deg prismatic hull. origonal power was twin 330bhp D's. Top speed went from 46mph to 54mph, and fuel economy improved at 35mph by about .33mpg. That is more efficient under 40kts. The bottom was modified to accept the drive so the improved performance may not be all due to the drive directly, but a net improvement none the less.