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Re: Roberta's Torpedo

Posted: Wed Oct 12, 2016 4:54 am
by Roberta
Thanks for the info, guys. It basically convinces me more that the trim tabs are the way to go. The racing cleaver props are designed to run partly out of the water. A three point hydro would benefit from a prop design like that, but I don't think my type of boat would. I doubt my prop ever will, or should, be exposed on my boat. A diagram used in the link shows an outboard that has a the shaft parallel to the water. I have a 14 degree prop shaft angle, which will inherently create stern lift. Being that loads and conditions can vary, I think being able to vary the trim is a better option.

Roberta :D

Re: Roberta's Torpedo

Posted: Wed Oct 12, 2016 5:22 am
by Bill Edmundson
Roberta

I vote with you. I played with the trim on the Bartender's outboard. I had good speed at WOT the first time. I backed off and played with the trim to get best economy. When I went back to WOT she started lunging. There's no one answer.

Bill

Re: Roberta's Torpedo

Posted: Wed Oct 12, 2016 5:56 am
by Roberta
Thanks, Bill!!

Roberta :D :D :D :D

Re: Roberta's Torpedo

Posted: Wed Oct 12, 2016 1:29 pm
by kens
Roberta wrote:Thanks for the info, guys. It basically convinces me more that the trim tabs are the way to go. The racing cleaver props are designed to run partly out of the water. A three point hydro would benefit from a prop design like that, but I don't think my type of boat would. I doubt my prop ever will, or should, be exposed on my boat. A diagram used in the link shows an outboard that has a the shaft parallel to the water. I have a 14 degree prop shaft angle, which will inherently create stern lift. Being that loads and conditions can vary, I think being able to vary the trim is a better option.

Roberta :D

Who suggested a cleaver prop for your boat? where did that come from?

Re: Roberta's Torpedo

Posted: Wed Oct 12, 2016 1:55 pm
by Roberta
Jenko's post had a link that described using a cleaver prop for high speed boats.

I have done a lot of research and looked at 4 different prop mfg's. None have a 13X13 four blade prop with a 1" bore that has rake values you describe. Not sure they would be suitable if they did. Cleaver style props are for different style high speed drag boats. Reduced, Zero, and forward raked props in a conventional blade pattern are for slower work boats. I have the tabs on order.

Roberta

Re: Roberta's Torpedo

Posted: Wed Oct 12, 2016 8:35 pm
by Rich Coey
I know props react different for different boats. I have run a federal, an OJ, and Acme. Acme seemed the smoothest for me. I have had four different Acme props. The two I kept were a three blade 13 x 12.625 for general use and cruising and a 13 x 11 when we are pulling skiers and tubes. I don't know what the rake is but I do know the more throttle you give it the more it lifts the stern. Unless the waves are just right ( or wrong) I have no porpoising up to 50+mph. By the way, Acme says their 3 blade props have the same surface area as their 4 blade, and are more efficient and a higher top end. Although they also said
( here we go again, different boats ) some boats with reduction gears perform better with a 4 blade prop.
Just have to try them out.

Rich

Re: Roberta's Torpedo

Posted: Thu Oct 13, 2016 3:14 am
by kens
The last I heard from Paul Kane, he is up to 60mph+ with a Michigan DynaJet, and he hasn't found WOT yet. (DynaJet is one of those so-called 'workboat' props.)

Re: Roberta's Torpedo

Posted: Thu Oct 13, 2016 5:12 am
by Roberta
Did you also notice that Paul's boat has trim tabs/cavitation plates? Used to keep the bow down. And the last I read on his site he was running an OJ prop with about a 7+ degree rake.

No one seems to know what the rake is on my prop and how a prop they suggest would be different.

Thanks, Ken and Rich. I don't have access to a big bag full of props to try out and not part of the Rockefeller family that I can just try them all out. The tabs will work. They were ordered long before this discussion was started by Ken.

Roberta :?

Re: Roberta's Torpedo

Posted: Thu Oct 13, 2016 8:45 am
by Jimbob
Just sitting in my office dreaming about boats. Looking at my pictures and just realized that the chris craft cobra has a similar look to the torpedo. Thought you might like to see the pictures.

Jim

Re: Roberta's Torpedo

Posted: Thu Oct 13, 2016 9:31 am
by Roberta
Cool! Thanks.

Roberta :D

Re: Roberta's Torpedo

Posted: Sat Oct 15, 2016 5:37 am
by SunFun
Roberta,
Before spending money on a "big bag of props" you might want try BBlades Prop Shop. They have a great national reputation working on props for outdrives. Anything from a 19ft runabout up to $15K props for the offshore guys. They also have a prop test program.

The best part is they are in your neighborhood, Princton WI.

I'm not sure how much work they do with inboard props, but with them so close, it would at least be worth a call.

Good luck!

Scott

Re: Roberta's Torpedo

Posted: Sat Oct 15, 2016 6:43 am
by Roberta
Thank you.

Roberta :D

Re: Roberta's Torpedo

Posted: Sat Oct 15, 2016 2:04 pm
by kens
I stand corrected, it was Bruce Dow that responded to a Paul Kane post; where the answer was a neutral rake prop.

"Prop Rake definitely was "the charm" for me.

I was running a 12x15, and my WOT RPM were just about perfect, but I had porpising in the top 20% of my RPM range.

Earlier in this thread, Mr. Hot Rod described a neutral rake prop that was dragging his bow down, so he swapped it out for one with more aft rake. (Look for the picture. It's the one with the red paint on it)

He sent me that prop to try.

Putting the props side by side showed a clear difference in the overall geometry. My original prop had pretty severe aft rake. The new one was "neutral". When I next bring the boat out of the water, I'll post pictures of the two props side by side.

And it did the trick. No more porpising. I did not need to modify my hull. WOT RPMs are still almost perfect for my engine spec."


In my discussion with Paul, he added the cavitation plates to overcome a severe moonshot when coming out of the hole. He didn't indicate any porpoising at speed.

Re: Roberta's Torpedo

Posted: Sat Oct 15, 2016 3:59 pm
by Mr Hot Rod
Yes, Ken, that prop was a perfect match to Bruce's boat. It even maxed out at the recommended WOT of 4000 RPM.
You won't find too many low or zero rake props in the used market. A custom prop builder may be able to help.

Our OJ Legend 3 blade 12x15x1 LH is running 40 MPH @ 2500, 60 @ 4000, 70 @ 4500 (Peak Torque) and 80 @ 5200. WOT is still unknown ...
Our second best prop is a Custom OJ Legend cut down to 11x14. The engine loves the increased RPM.

The trim tabs are just another tool to dial in the ride. Before we added our cavitatio plates, the hull would jump 12" out of the water when
stabbing the throttle at 40, 50 or 60 MPH. The boat always landed perfectly but ran a little loose. With the cavitation plates, we can do full 6000
RPM launches with minimal hop. Adding a bit of down pedal forces the bow down when you want to flatten out the rough stuff.

Related links :

____________________
Paul Kane
Kane Custom Boats Ltd.
Chelsea, Quebec

Building the Glen-L Hot Rod : http://www.kanecustomboats.com

Glen-L Boat Video Directory : http://www.kanecustomboats.com/pages/vi ... ctory.html

Re: Roberta's Torpedo

Posted: Sat Oct 15, 2016 5:36 pm
by Roberta
That is really what I am trying to do with the trim tabs. Get the bow down in the rough water to smooth things out. Otherwise at higher speeds I'm launching over the top of waves and chop. I've had the boat over 50 mph with no problems until I hit chop or waves. I need the aft rake to get the heavy bow out but I also need to be able to keep more of the hull wet at speeds. The tabs are my best compromise.

Thanks for all the help and support.

Roberta :D