Hi Scott.

Thanks for your advice, though I do not understand all of the tech terms.
Anyway I still have doubts for my part.
But maybe you can help me out?

Here's info about the wooden boat, I am building:

Deep Vee Mono.
Lenght of hull: 56 inches.
With of hull: 12 inches.
Engine: Blata 40.
Hp.: 13,4.
Engine rpm.: 17.400
MHZ gearbox for two drives.
Drives: MHZ double stern drive.
Stern drives vertical angle adjustable (also by remote).
Rpm. at props: 26-27.000.
Expected dry weight: Less than 14 kilos.

I don't know if the sterndrives comes with recommended props.
But before I put on the stern drives, I have to take a stand about the surface piercing issue.
Also consider that the boat is meant to run in rough waters. A fast and steady run is more important than fast turning abilities.

Your advice is very welcome!

Cheers!

Woodie.

PS: Isuzu. SORRY. I should have put this in my own tread (Cigarette).

Woodie, by you putting it here, saves me from having to thread jump to get the same answers I'm after...no problem!!!! Thanks for the article Scott. I did a little more reading after that, and I'm convinced..That's why I ask you!!! I never ran my shockwave in rough water... but it was a good 5-7 mph faster with the surface drive, using a stock Zen and a header that was too long not allowing the motor to come up on the pipe!! Except for my run against Woodie... almost all of my running will be done on glassy to 3 or 4 inch chop. So I'll set it up with that in mind... and take what I can get in the rough water run!!

Woodie wrote:
Running OVER DRIVE gearbox is ... well not very efficient at all because torque loss's at props has torque less than half what engine is producing.
Your going to have too run SMALL props snyways, so to get small props with limited surface area hooked up pushing a big & heavy hull you have to bury the props in the water where cavitation will be minimal.

I will go find the thread over at Jims "JRCBD" about another inquire made using over drive, it had input from some with far more mater of fact tech than I can offer here .... Will add to post

Need to be an JRCBD member to read, but a LOT of info was shared here: www.jrcbd.com/showthread.php?t...light=overdrive

Hi Scott.

Thanks for your patience with me.

You give me a lot of fine inputs about the princips about engine/drive.
But I am still not convinced to give up my idea of the drive setup on my boat.
Remember that the Blata 40 is a brute power beast with much more torque than zenoahs, and it NEEDS 2 drives trough a gearbox in order not to rip the stern drive(s) apart.
I agree about the smaller props. I have put a smaller prop with a higher rise on my real speedboat, and actually got it to run 3-4 mph. faster. Of course with a submerged prop as allways.
But I still don't understand why MBG's should/could run faster with a surface-piercing prop, when no real boats seems to use this?
Am I wrong, or getting too wise (again)?

Cheers!

Woodie.

PS: Forgive me if I am getting a little stubborn.

You must have missed the LAST paragraph of the link I first shared ?
I am NOT trying to convince you of anything .... simply providing you with information. What of it and how you use it is your choice to make ... Toy boats toy boats

Woodie wrote:
after fallowing these questions you are asking I might say it sounds like you need to do some Google searching on this topic !!!!!
your question has been answers and you continue to argue and say you know your ideas are right... so go dump a bunch of money and prove yourself wrong..

Woodie wrote:
The weight/power ratio of real boats as opposed to our boats is totally different, thus prop/drive selection are also totally different. Also we run at scale speeds way beyond the speeds of real boats. Keep that in mind!

Hi Marc.
Honestly I am not convinced, so for a start I will go for smaller submerged props. After all its no problem to change the setup by raising the drives about an inch, if I should be proven wrong.


JTD:
You are impolite. I don't like that.


Woodie.

A few more pics....

Wow!
That really is coming along mate!
Gonna be a nice big boat when finished!