CD25D Prop Happiness?

[AMcC]

I'm not thrilled with the prop on my CD25D - just doesn't feel like it gets any real 'bite' and I don't get anywhere near hull speed under power... mine isn't original - and is a 3-blade Michigan Prop 12 R 08. Looking for what others are using with success/happiness, and/or suggestions... planning to cruise up Hudson River and through locks to Lake Chaplain this summer, so a happy prop would be helpful...
-Alec

[Dick Kobayashi]

I suggest you search this Board for a post by John Vigor who investigated this matter thoroughly, I recall. Post was in the early 2000s. Since John is famous in Cape Dory world I would take is obs seriously.

[sgbernd]

It depends largely on the engine and transmission you have. When I re-powered, replacing the MD7B 17hp with a Beta-16hp, I specified a Michigan Wheel cruising prop. The boat yard disregarded my written instruction and and installed an ACME prop, the smallest one ACME makes, because, in the installer's opinion, "that is what we are using". Translation: "the local dealer stocks and supports them and we have had good luck with them".

I was cranky that he had not done as instructed, and ACME builds ski/wake boat props rather than sailboat props, and the prop looks like a ski boat prop rather than a sailboat, but after using it, I confess he was right and I was wrong. While I gave up 1hp in the repower, and a bit of fuel consumption (0.25 gph to 0.265 gph), the boat now feels both under propped (it is) and over powered, cruising at 5.5kts with a top speed of almost 7. In retrospect, I could have used the next smaller engine (14hp) and the same prop and achieved an identical outcome.

I could not be happier. My only complaint is that the increased prop thickness compared to the Michigan Wheel means I have to pull the engine forward to remove the prop as the aperture size is designed for the thinner, larger MW, but otherwise, everything is good.

https://acmemarine.com/

Steve

[Dick Kobayashi]

Just another thought. Make sure you know the hp of your engine. The CD 25Ds were typically powered by Yanmar 1GM engines. When I bought mine it was listed as having a 7.5hp engine but when I scraped the crud off the engine and plate I found I had a 6.5 hp engine. The Yanmar GM series ran, I believe, from 6.5 to 10 hp. Advice: Make sure you lay your own eyes on the mfg plate.

You will need to know this with 100% certainty to discuss and consider prop options.

These boats are heavy and have small engines, so small changes or small mistakes can have an effect on performance esp. in a head wind or head current situation. The Hudson is a river and it is tidal to Albany, so...

[n5ama]

I am using the original prop that came with my boat. It has a Yanmar 1GM engine and I presume is 6.5hp.
Is there any feel for the performance of the stock prop versus a aftermarket prop, ie is the original prop a known problem?

Thanks,
Tom

[Cathy Monaghan]

You might have the correct prop and it just needs to be repitched. Whether your boat is over or under propped or pitched you may find this article of interest:

https://www.oceannavigator.com/are-you-over-propped/

[sgbernd]

Not to rain on the parade, but if I understand correctly, a rule of thumb for sail boats is ~1hp/500lb displacement. If a CD25D weighs a bit north of 5000lbs dry, that would mean 11hp. If you have only 6.5 or even 7.5, the problem may not be the prop, rather, it is just under powered. Also, add the fact that the engine may be tired after a few decades.

If such is the case, playing with the prop will only prove an expensive form of entertainment but is unlikely to improve performance significantly.

Steve

[n5ama]

Hi Steve,
Thanks for the help, but the question for me is (given the boat, engine and the prop that came with the boat) is there some common wisdom (with CD25D owners) that recommends another prop versus the stock unit.

I know the boat is underpowered but is there a better way to help this situation short of spending $$$$ to replace a engine that is running like it should?

Tom

[RC James]

My 25D came w/a 12" 2 blade and the previous owner had Michigan 12" 3 blade in a box of extras. The 3 blader was pitched at an ungodly 12", so w/a little internet sleuthing, I decided on repitching to 9". 1982 boat w/smaller Yanmar engine.

Moves boat at a comfortable hull speed of 6-6.5 at mid-revs.

3 blades might re-ignite the lock/unlock discussion (hope not), but since I don't long distance cruise, I'll settle for whatever slight speed loss I may incur for a wheel that seems to give a smoother ride and seemingly more maneuverability under power than the original 2 blades.

[n5ama]

My 25D came w/a 12" 2 blade and the previous owner had Michigan 12" 3 blade in a box of extras. The 3 blader was pitched at an ungodly 12", so w/a little internet sleuthing, I decided on repitching to 9". 1982 boat w/smaller Yanmar engine.

Moves boat at a comfortable hull speed of 6-6.5 at mid-revs.

3 blades might re-ignite the lock/unlock discussion (hope not), but since I don't long distance cruise, I'll settle for whatever slight speed loss I may incur for a wheel that seems to give a smoother ride and seemingly more maneuverability under power than the original 2 blades.

Thanks for the insight!!
I have no idea what the stock prop pitch is and didn’t even know they could repitch a old prop.
My boat is good for 6 on a good day without a headwind. It does this without heavy panting so I suppose its ok.

Tom