"Reverse" on a CD30--Will a three-blade prop help?

[Geoff Safron]

It's widely known how miserable the '30 with the MD7A is in reverse...Has anyone managed to do anything to improve the situation? I understand a tri-prop would belp, but there's a trade-off in water resistance. I'd appreciate any empirical test data!

While I've got you: Has anyone made their own: 1) Cockpit cushions; 2) Dodger and/or Bimini? Looking for good designs and a "cheap" source of Sunbrella by the yard...

Thanks to all!



Pixel179@AOL.com

[Jon Larson]

Geoff,

Some years ago I contacted Cape Dory and asked about the three bladed prop. Their response was that I would get noticably better reverse thrust with the three bladed prop and they assured me that I wouldn't notice the difference in drag when under sail.

I've a friend with a CD30 who did put on a three bladed prop, and I notice that there seems to be less vibration and less noise with her prop on her boat.

Cape Dory's prop was a custom modified jobbe, by the way. I believe it was Columbian that they recommended as having the closest prop for the CD30, I may be wrong in that.

I don't think anything will do much for directional control when in reverse in these boats, however. Put it in reverse and you've to a large extent put your future in Allah's hands no matter what. Backing out of a slip into a stiff tidal current still gives me white knuckles and cold sweats and I avoid those situations like the plague.

I guess I regret not going with the three bladed prop, but after nearly 16 years with this boat, I also think I've fairly well learned how to avoid the situations where I am very dependent on strong reverse.

Jon Larson
Cape Dory 30 PERI
San Francisco Bay

It's widely known how miserable the '30 with the MD7A is in reverse...Has anyone managed to do anything to improve the situation? I understand a tri-prop would belp, but there's a trade-off in water resistance. I'd appreciate any empirical test data!

While I've got you: Has anyone made their own: 1) Cockpit cushions; 2) Dodger and/or Bimini? Looking for good designs and a "cheap" source of Sunbrella by the yard...

Thanks to all!

jon9@ix.netcom.com

[Olli Wendelin]

Geoff,

I have a three bladed prop on my CD 30. Don't know the specs on it, but will check on my next hauling (~1 yr?). The boat sails well, but I don't have a two bladed prop to compare it with. Of course with a two bladed prop you would have to mark the shaft and lock the prop in a verticle position when sailing to have any advantage. My three blade provides good thrust in forward and reverse. I only use reverse to stop the boat, not to drive it backward. Single screw vessels in general tend to steer to port when backing, sometimes you can make them go dead astern, but not to stbd.

In answer to your question, a three bladed prop may help you to stop quicker, but probably would provide little change in control when backing.

Olli Wendelin
Cape Dory 30
BLUE MOON
Charleston, SC



wendelin@spawar.navy.mil

[Paul Grecay]

I have a CD 28 with a Volvo Penta MD2B (24hp). I switched to a three blade prop with positive results. Because of the greater thrust, I find that I have a great deal more control in backing primarily because I can stop the boat if it is not backing properly. I have also found that "eventually" it will steer in reverse once I get some backward speed...this is to say that I can gain some control over where the stern is going. When backing, the bow will eventually swing opposite to the direction I'm steering the stern. For example, with the tiller hard to port, the stern will begin turning to starboard and the bow will begin to swing to port. Again, I need considerable space behind me and none of this will overcome a stiff breeze or current. Since my boat is at a mooring, I have some manuvering room. My advice is to go with the tri-prop because it gives you more stopping power if you get in a jam, not because it gives you greater directional control. Also, take the boat out on a dead calm day, position yourself near a buoy or some other reference point, and practice. By the way, my prop is a Michigan Wheel 14LH pitch=6...I will have it pitched up a bit since the engine can handle more).



rfurman@dmv.com

[Neil Gordon]

Has anyone made their own: 1) Cockpit cushions; 2) Dodger and/or Bimini?

You might try cushions, but I suspect that making your own dodger would be nearly impossible. My sailmaker gave up dodger work because of the effort involved in measuring, cutting, fitting, etc., etc. There's a reason dodgers are as expensive as they are.

Neil
s/v LIQUITITY
CD28 #167



nr_gordon@compuserve.com

[Gary, CD30K Ariel]

I have a three blade prop, 13LH12. It seems to go in reverse well. Turning is still a slow process, but I can control the boat. The three blades are smoother running because two blades are always in the open water while one is in the keel opening and they are easier to balance. Be sure to lock down the transmission in reverse or the blade will spin and increase the drag. You might be able to find a three blade feathering prop and forget about the drag. A friend has one on his C&C 35 and loves it.



gary.rogers@nashville.com

[John]

It's widely known how miserable the '30 with the MD7A is in reverse...Has anyone managed to do anything to improve the situation? I understand a tri-prop would belp, but there's a trade-off in water resistance. I'd appreciate any empirical test data!

While I've got you: Has anyone made their own: 1) Cockpit cushions; 2) Dodger and/or Bimini? Looking for good designs and a "cheap" source of Sunbrella by the yard...

Thanks to all!

Here's my two cents. On our 30 we installed a Michigan 3-blade, I don't recall the diameter or pitch at this time. I can tell you we increased the diameter over the two blade by as much as possible. The results are more thrust in reverse but still quite limited. I believe this to be a factor of horsepower not propping. Our boat loaded weighs about 12,000# and the Volvo MD7B the wonderful engine she is at 12hp just can't handle that. At next haul we may go with a CDI or similar prop that reportadly makes great gains in reverse over standard designed props. I don't know if it can compensate for low horses though. Cape Dory should have installed a 18 or 20hp at least. We pray a lot when we are reversing and like others sure avoid risky situations. I do find a straight helm position held until good momentum is gained is a must before cranking the rudder over. I don't find prop walk is much of a problem unless you're running up the RPM's before momentum is made.

[Ed Carlson]

Jon

My wife and I purchased our 1980 CD30 Ketch in the Fall of '95. We found the original Volvo Penta engine in pathetic condition and way underpowered. We replaced it with a new Universal 23 hp, 3 cylinder, which fit the engine mount footprint very well, and gives us excellent power. We also fit it with a 3 blade screw. However, we still find controlling the boat in reverse to be a challenge. So I must endorse your observations that it has a mind of its own coming out of the slip.

Ed Carlson
CD30 Skywind
Satellite Beach, FL



SkywindMCM@aol.com