Right boat, wrong prop ?

[rockborn]

i have just purchased a 1980 Morgan 462 with a 62 hp perkins . while having the cutlass bearing replaced i asked the shop to refurb the prop. they told me they think it is the wrong prop and they need to know the max rpm, the gear box ratio and hp. how can i get this info? thanks

[Bash]

You'll find the max RPMs in the owners manual. The gear box ratio is often stamped on the tranny. Tell us what transmission you have, and somebody here probably knows it offhand.

Congrats on the new boat, by the way.

[Bash]

just in case you don't have a manual, assuming the engine is a 4-154: http://www.kp44.org/ftp/Perkins_4-154_Shop_Manual.pdf

is your tranny a Borg-Warner 1:1.91 Velvet Drive?

(And hows come the fellows in the prop shop weren't able to find this out for you? Don't they have access to the boat?)

[rockborn]

good question, i had just received an e-mail from the shop about this issue. doesnt anyone use phones anymore? i dont have a manual, would like to get one.ill get some more info, thanks

[hpeer]

Going thru the same thing as we speak (erh, type. )

I have a ZF-30, the gear ratios are on the plate. But I got a bit confused with that because they list forward as "A" and reverse as "B." I know the transmission came with two different possible gear ratios and I "thought" A and B meant what variant of transmission it was.

Took a little while staring at the manual to figure out what they were talking about. It could have been written a little more clearly and I could have been a bit less dense.

[delmarrey]

It seems the shop must know the motor and trany specs. Otherwise, why would they think it's the wrong prop?

[GordMay]

Originally Posted by hpeer

... they list forward as "A" and reverse as "B."...

That's the "usual" standard configuration; but it could be reversed, such that A is reverse, and B is fwd.

[delmarrey]

Originally Posted by GordMay

That's the "usual" standard configuration; but it could be reversed, such that A is reverse, and B is fwd.

For ZF trany's A= AHEAD. The fwd will be the higher ratio (e.g. 2.36:1 fwd vs 2.0:1 rev). The prop will spin faster in rev.

[SkiprJohn]

The question would be, "Why does the shop think it is the wrong size?"
It is good to know all those specifications anyway but what are the clues that make the shop think it's wrong.
Perkins and Velvet drive are a very good combination but the prop size is determined by HP, RPM, trans Ratio and length of the waterline of your boat.
Do a search of "Proper Prop Size."
kind regards,

[rockborn]

he prop shop thinks the diam is too small and the pitch too steep. ey feel is a powerboat prop. no wonder it went 7.4 knots during sea trial under power. thought i had a fluke.

[David M]

What is the pitch, diameter and the number of blades?

Is your engine able to reach full governed RPM?

Is the engine healthy and the bottom clean?

[SkiprJohn]

7.4 knots would be pretty close to hull speed in calm water. That should be easily doable for your boat with a good sailing prop too. At what RPM was the engine at that speed? A powerboat prop would not give you best efficiency at slower sailboat speeds. If the prop is 2 or 3 blade 19 to 21 inches in diameter and pitched at 12 to 15 then its probably a sailboat prop. If quite a bit smaller diameter and pitched higher then it could be a power prop.

Indeed, a prop shop should know what they are talking about so if it looks too small and has a high pitch they are probably right and you should think about a new, more efficient prop.

Good luck in sorting it out.

kind regards

[hpeer]

Originally Posted by delmarrey

For ZF trany's A= AHEAD. The fwd will be the higher ratio (e.g. 2.36:1 fwd vs 2.0:1 rev). The prop will spin faster in rev.

For the ZF-30 there are two possible configurations:

A = 2.15 and B=2.63 OR
A = 2.70 and B=2.63

I have A = 2.15

http://www.tadiesels.com/transmissio...es/ZF_30_M.pdf

I would have thought the 2.70 would have been more appropriate for our very, very heavy boat. (40,000lbs)

Just as with the OP, the prop shop said my 3 blade 19x13 was a "planning power boat prop." The are recommending a 3 blade 21x12 "sailboat prop." The difference is in the curvature of the blades?

[David M]

I think you might be getting a load of bull. They don't seem to know all of your boats variables. Did they even ask the most important question of if your engine can reach its full RPM?

Are they the ones who would be selling you a new prop?

High or low speed props are primarily determined by the ratio of the diameter to the pitch. High speed props have a greater pitch than diameter, in inches. Your prop has a greater diameter than pitch.

You can run all the calculations you want but again, the most important question that needs to be answered is if your engine can reach its maximum RPM. Calculations can be wrong, but being able to reach max RPM is an absolute must.

[hpeer]

Yes they asked, I sent them the 2 page spec. sheet for the engine.

They also asked for the gear ratio and the particulars on the boat.

This Yanmar 4JH4-TE (turbo) reaches full 75 HP at 3,200 rpm.

It reaches 70HP at 2,600 rpm. Sorta flattens right out at the top end.