CD 30 Propeller Size

[Fergus]

I would be grateful if someone would post the propeller dimensions for a Cape Dory 30C.

[Ben Thomas]

Fergus, tell us the engine BHP and gear ratio of the transmission. There were some pretty standard combinations that the 30 came with.
We have the lwl and displacement already.
Ben

[Fergus]

Thanks for the quick response. Unfortunately, I am not sure the information I have is particularly correct. There was a severe lack of documentation when I aquired her.

The back story is that the existing engine, a Volvo MD7A, has developed a problem that I have decided requires me to re-power due to a total lack of spare part availability in Scandinavia. I guess I could probably chase down the parts somewhere, but I would prefer to avoid any future parts issues.

I understand that this is a standard installation, i.e. a V-drive driven by the Volvo gear box which I presume, based only on the gear box length, is a 1:1 reverse gear arrangement. I need the propeller size as input to the people that will supply the replacement engine which (so far) will be a Beta 16 bobtail.

I am pretty ignorant when it comes to engine and propulsion issues so I have been hoping that I can get the information I need without having to take her out of the water.

[Larry DeMers]

Hi,

We have a CD30c, 1983 vintage, #283, and it uses the Volvo MD7b engine with V Drive. She has a 13x13R prop, but is underpowered with this prop. Could use a 13x14 or 15 R.

I suspect that this is what you have on your boat, given the engine and v drive combo.

Cheers,

Larry DeMers
s/v DeLaMer
CD30c Sailing Lake Superior

[Ben Thomas]

Fergus,
If you used the v-drive that you can order with your Beta 16, a 2.13:1 gear ratio A 13 x 9 or 13 x8 Three blade right hand turn prop will do nicely.
Do you plan on re-using your existing v-drive? Or why the Bobtail? The Bobtails come with no transmission, no adaptor or drive plate.
Ben

[mattlydon]

tell them the boat, the engine and the trany ratio's, and they'll be real close on guestimating the right prop for you.

They can also re-pitch it at a moderate rate if it's off a bit.

Matt

[Ron M.]

Had to deal with this with a re-power a few years ago. My recollection is your prop size will be limited to the aperture of the keel/rudder. I had 2 or 3 prop shops establish proper size using the established formula and all suggested a prop too large in diameter - 14". A 13X13L Mich. 3 blade gives me about an inch of clearance at the top of the cutout. The 14" would fit but the less clearance would effect performance,(so I was told and it made sense to me). I have absolutely no complaints with this set up. Under normal conditions hull speed is maintained with less than 2k rpm. 19 hp volvo/zf v-drive.
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[Ron M.]

Had to deal with this with a re-power a few years ago. My recollection is your prop size will be limited to the aperture of the keel/rudder. I had 2 or 3 prop shops establish proper size using the established formula and all suggested a prop too large in diameter - 14". A 13X13L Mich. 3 blade gives me about an inch of clearance at the top of the cutout. The 14" would fit but the less clearance would effect performance,(so I was told and it made sense to me). I have absolutely no complaints with this set up. Under normal conditions hull speed is maintained with less than 2k rpm. 19 hp volvo/zf v-drive.
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[Fergus]

Thanks everybody, for your very useful replies.

Larry, I suspect you have pretty well nailed the engine/power train configuration - our boat is hull number 255.

The bobtail approach is based on the people at Beta Marine claiming to be able to supply a engine that will bolt on to my existing transmission. They have mentioned Cape Dory and the Volvo MD7 so I am cautiously optimistic.

Work has been intruding on my recreation, so I will defer the engine change to the winter, when we will have her on the hard.

Again, thanks for the good information.

[Maine Sail]

Fergus,

The most important thing is tht you size the prop to attain as close to max rated RPM at WOT (wide open throttle) as you can.

Universal uses Kubota blocks and say's this:

From the M-25 XPB Spec Sheet:

"Universal recommends a propeller that will allow the engine to turn 3000 RPM underway at full throttle"


Max rated RPM for that engine is 3000. Universal & Westebeke are very picky on proper RPM. In the spec sheet for all their new engines they will have a statement like the one above. The Universal engines use Kubota blocks just as Beta does.



This is a direct quote from Beta US.

"When operating under WOT (wide open throttle) your engine should operate within 200 RPM of the manufacturers specification."

Beta is a tad more liberal than Universal/Westerbeke on this but still want to see it within 200 RPM. My own engine is within 50 RPM fully loaded with a clean bottom and prop at WOT and the engine has 3K hours and runs as good as a new one. It took two tires for Campbell to get it right. The first try she was off by 300 RPM which is totally unacceptable.

You should be able to turn at a minimum 3400 with 3600 being max rated for the Beta 16. Personally I'd want a prop no more off than +/- 100 RPM of max rated.

You'll also want to first confirm your tach is accurate with a digital photo electric tachometer as they can often be off being tachometer driven. Digital photo tachs are quite reasonably priced these days compared to when I bought mine.

[Sea Hunt]

On a Cape Dory 30 cutter rig (not the ketch) with the Volvo MD7A (13 hp) and "V drive", is it possible to re-power with a diesel that has a standard engine installation and configuration with the engine "facing" (for lack of a better term) the bow

Or, because of the configuration and design of the engine compartment, etc., is it mandatory to use the "V drive"

If a repower with a standard engine configuration is possible what would be some engine recommendations for engines from Yanmar, Westerbeke, etc.

Any ideas on rough guess approximate total cost to remove current engine and "V drive", buy a new engine and installation

Thanks in advance

[Ben Thomas]

We are pretty much stuck with the v-drive, to change the configuration means major demo of companion way landing and steps and extension of existing beds, the whole thing would protrude into salon and be way to high to match up the angle of prop shaft even with a down angle transmission. Just not worth the effort.

Estimate of cost for just the Beta 16 or 20 with the ZF 15 MIV v-drive 2.13:1 gear ratio
list price for Beta 16 $8249.00
List for v-drive $3870.00
Adaptive stringers $325.00
Total list $12444.00

CDSOA discount $2115.48
CDSOA cost 10328.52

The Beta 20 List $8770.00
v-drive $3870.00
Adaptive stringers $325.00
Total list $12965.00
CDSOA discount $2204.05
CDSOA cost $10760.95

Add freight depending on location at least $185.00 on east coast
The adaptive stringers are bolt/glass on. no changes to existing beds.
Can't help with removing or install costs. Although the install should be very straight forward and easy using my stringers.
You will need a longer prop shaft. as both of these engines will sit further forward and a little higher than the Volvo
Beta 20 13x9" RH three blade
Beta 16 13x8 RH three blade
Hope that helps
Ben

[Sea Hunt]

Hello Ben:

Thank you very much for the information. I guess I kind of thought it would be very expensive and structurally impossible but I needed confirmation. Thanks.