CD25 prop size

T

Tom on Icarus

New member
Joined
Sep 15, 2007
Messages
175
Reaction score
0
C Dory Year
2008
C Dory Model
25 Cruiser
Vessel Name
Tranquil~C
I have a CD25 with a Yamaha 150. Is there a prop that is best for general use? I tend to run more to the heavily loaded side than the lightly loaded side.

Cheers, :beer
Tom
 
Tom,
We would have to know what prop size you are running now. What the top RPM are currently when loaded, and what the top speed is when loaded. If you are hitting the Rev Limiter, and not getting enough speed, then you may be under propped. If you cannot hit the specced WOT, then over propped.

The Yamaha 150 is a strong engine, and I would suspect that a 15" pitch prop would be close. It would also depend on the prop material (ss has less deflection than the aluminum)--cup in the prop, number of blades, altitude etc.
 
I seem to get about 5200 RPM at WOT with the 15" aluminum prop that I have.
My question was to see if any of the Brats have tried different props and found one to be the best for the unit under the conditions described. As mentioned, I am usually fairly heavily loaded.

Cheers, :beer
Tom
 
We recently repropped Muse. We chose a stainless Michigan Apollo 3-blade, 14-3/8 diameter, 15 inch pitch. (The aluminum prop we replaced had a 15-inch diameter.)

It seems to be a good choice, and our Honda 150 appears content. Our WOT RPMs hover around 6500 -- although I like to cruise between 4400 and 4800 RPM.
 
Ron,
The accepted WOT for the Honda 150 is 5,000 to 6,000 RPM. I guess I am a little surprised that you are hitting 6500. I thought the rev limiter was set at 6,000.
 
thataway":15svd8za said:
Ron,
The accepted WOT for the Honda 150 is 5,000 to 6,000 RPM. I guess I am a little surprised that you are hitting 6500. I thought the rev limiter was set at 6,000.
Click to expand...

Hmmm ... I really thought that's what the tach indicated, although I suppose I could have misread it. I only ran WOT once, to check the new prop..

I'll try again, next time I'm out.
 
If the boat was empty and the water smooth, I would believe the 6500 RPM. What were the knots? ~25? It's kinda bouncy with a flat bottom unless it's really smooth.

I run a 16" pitch prop on Journey On, though we cruise. It tops out at 5500, semi-loaded. Its the 4 blade version of the stainless Apollo. LH rotation on top of that.

Boris
 
Tom

A couple of other things to consider. How high is your motor mounted? I have yet to have a motor mounted properly by a dealer. They generally all mount them too low. Having owned two C-Dory's and helping adjust a third, you need to look at the motor when the ventilation plate is parallel to the bottom of the boat. That plate should be at the same level of the bottom. I use a carpenters level to project the bottom of boat back to the ventilation plate. The other is the way you measure WOT. I generally push the throttle up to the stop and then start trimming the motor up until the prop ventilates (sucks in air). That RPM is WOT.

On my Yamaha 150 on the CD-25, when heavily loaded, WOT is about 5600 RPM. I say about because at about 32 mph, I start porpoising at 5400 RPM, but the prop has not yet ventilated. The prop I am running is a 4 blade Solas stainless steel in 15 pitch.
 
The only think I would question about Tom's post is trimming so that the prop ventilates. My feeling is that a properly set engine in smooth water should not ventilate. (Tom says he has not ventilated --but the boat porpoises--my 25 was under powered, so we never got to that speed)

But I would also comment that to check WOT the trim tabs should be fully retracted. Putting trim tabs down, will often stop porpoising. But porpoising is usually due to a hook in the bottom or a design issue. As many of us say, over 30 mph the boats become more difficult to handle,
 
Bob,

My porpoising is more a loading issue than anything else. For some reason when the water tank forward is full or near that, I will porpoise above 32. I had the boat up to 35 mph in water with a little ripple on top this spring with no water on board and it was a smooth ride at 5600 rpm. As soon as we hit the glassy smooth water we dropped back to 31-32 mph.

I did forget to mention the trim tabs.
 
I can understand the trim of the water tank causing this. I have also had the ripple effect a number of times...it even works in the cats!

My Caracal is a boat known for ventilation (as are most single engine cats), and there are "cures"--not all of which have I affected (jack plate, and permatrim). But ventilation is disconcerting when running fast--and not particularly good for the engine or prop.
 
Back
Top