10/10.8 Meter Mid Cab. Prop and Running Gear

[todd brinkerhoff]

I may be the only 10.8 Express on the forum, so I figured I'd ask the 10M MC folks. What reduction gear are you guys running in the V drive, and what prop size and angle have you found best.

Stock gear on the 10.8 V-drive is 2.5 with the crusader 7.4l (350 hp) with a 22X22 3 blade prop. I am planning on changing out the small trim tabs to something larger, but wanted to know what your thought on size and pitch for the best performance for your MCs.

Is there a significant difference between 3 and 4 blade?

Does cupping make much of a difference?

WOT is about 4000, at between 26 and 27 mph with the current set-up. Boat dry is estimated at 17,500 lbs.

[BobCT]

Todd,

The midcabins are straight drives, 1.52:1 reduction spinning 3 blade 16x17's.

Sherman has the same boat I do and changed to 4 blade and looks like he picked up a couple of MPH at cruise.

Now that I've got some concrete #'s, I might do the same altough he was going to get his cupped a bit more.

WOT is around 4,000 for me as well at roughly the same speed. Not sure if this is much help considering the difference in transmissions and props.


Bob

[rbcool]

Don't know where you guys live but if your on the Chesapeake try Mark Goode at Goode marine. Him and father are MASTER propmen. It's amazing what these guys can do.
Ron

[RWS]

FWIW my NON mid cabin model came with BOTH 4 blade bronze and 3 blade nibral.

The 4 blade props did better overall, the 3 blade nibrals got a slightly better top speed.

RWS

[S.A.M.]

Todd,

What I've been able to find out is that the midcabins max rpm, by design from Trojan on the Crusaders, due to the weight, is 4000 with the 17x16 wheels.

With my new 4 blades (17x14) I can get 4250 out of the engines, but my top end is the same @26mph. If I cup the wheels I'll possibly get a higher cruise & top end, dropping my rpm back to the 4000 range.

I highly recommend 4 blades. They smooth out vibrations and lift the stern a little. 22x20 will be in the range you'd need. Just make sure you get a prop company that can run the numbers. Document your speeds at idle, 1500, 2500, 3000 & wot. They will need those plus the boats wet tonnage.

Good luck.

[todd brinkerhoff]

Hey Sherman,

Thanks,

What kind of prices did you get for the 4 blade bronze screws? I will probably post another topic line to see what you guys have done to improve overall performance of your international.

Todd

[S.A.M.]

Todd,

I purcased mine through http://www.getaprop.com/

Bob has put larger trim tabs on his boat and mine are the originals. This spring I'll replace with larger. My preformance should increase because I won't need as much of the tab down to run more level.

[gardnersf]

Hmm, My 86 Midcabin spins up to 4400 with Crusader 454's I assumed the props were original. They are 3 bladed.

[prowlersfish]

Todd,

What I've been able to find out is that the midcabins max rpm, by design from Trojan on the Crusaders, due to the weight, is 4000 with the 17x16 wheels.

With my new 4 blades (17x14) I can get 4250 out of the engines, but my top end is the same @26mph. If I cup the wheels I'll possibly get a higher cruise & top end, dropping my rpm back to the 4000 range.



Good luck.

If Trojan set it up to turn a max of 4000 rpm then Trojan ( like most builders )got it wrong . Always prop your boat to turn what the engine builder says not the boat builder . Boat Builders almost always over prop there boats as the what the highest top speed on a empty boat . ( all for sales as people buy speed numbers ) the builder do not care if engines fail early they want to sell boats . and over proping won't save fuel . you want to last ? prop it right

remember your boat is heaver then when it left factory , you would be surprised how much you gear /toys etc weights .

On gas engine they give you a max rpm range prop it in the range.
On diesel engines you want to prop it turn turn above the rated rpm

[prowlersfish]

Hmm, My 86 Midcabin spins up to 4400 with Crusader 454's I assumed the props were original. They are 3 bladed.

your proped right .