Hull speed and rpms for CD 31

jen1722terry · Post by **jen1722terry** » Aug 14th, '17, 15:18

Hi members,

Can any of the CD 31 owners tell us what rpms their engine requires to move the boat at the calculated hull speed of 6.46 knots?

We're still having some issues with our new engine and would like to compare its performance to other engines on similar boats.

Thanks so much,

Jenn and Terry

rorik · Post by **rorik** » Aug 14th, '17, 15:45

Hull speed and rims for CD 31

Not rims, yo... "dubs"

Sorry, couldn't help myself....

Capt Hook · Post by **Capt Hook** » Aug 14th, '17, 16:20

I don't think my CD-31 reaches that speed at full throttle.

moctrams · Post by **moctrams** » Aug 14th, '17, 18:24

https://www.easycalculation.com/physics ... ulator.php

Jim Walsh · Post by **Jim Walsh** » Aug 14th, '17, 23:07

jen1722terry wrote:Hi members,

Can any of the CD 31 owners tell us what rpms their engine requires to move the boat at the calculated hull speed of 6.46 knots?

We're still having some issues with our new engine and would like to compare its performance to other engines on similar boats.

Thanks so much,

Jenn and Terry

With a clean hull I attain hull speed at 2400 RPM with my 25 HP Universal M-25XPB. My max RPM is 2700. I have a three bladed Michigan prop which I believe is 15 RH 12. The stamping on the prop is unclear so I can't be positive.

jen1722terry · Post by **jen1722terry** » Aug 15th, '17, 15:24

Thanks to all for the comments on hull speed and engine performance.

Our new Beta Marine 25 presently needs about 2700-2800 rpms to get to hull speed, which may be a concern, not yet sure. Top end rpms were at the rated 3600 on July 29-30, but we're not presently able to get over 3200 without coolant venting from the pressure cap and rising engine temps ( approached 190 degrees before we throttled down to cool it off).

The Derecktor/Robinhood mechanic is due to come here to Northeast Harbor on Friday to again inspect the engine. We're very disappointed, as we've now lost two months of our summer sitting on the boat and waiting. Such is life, and our spirits are otherwise good.

If any of you stop in Northeast, look us up. We're on float 306 near the Morris Yacht yard.

Cheers!

Jenn and Terry

jen1722terry · Post by **jen1722terry** » Aug 17th, '17, 09:25

Hello friends,

We're writing specifically to ask for ideas from the many expert professional and amateur mechanics in our group.

Our new Beta Marine 25 was installed over the winter of 2017 at the Derecktor/Robbinhood (D/R) yard in Maine. We believe this was the first Beta Marine installation performed at D/R (they just received the Beta dealership in 2016). The boat was launched in late June and the new engine still is not performing well. It presently needs about 2700-2800 rpms to get to hull speed, which may be a concern, not yet sure. Top end rpms were at the rated 3600 on July 29-30, but we're not presently able to get over 3200 without coolant venting from the pressure cap and rising engine temps ( approached 190 degrees before we throttled down to cool it off). Bottom is clean and raw water inlet and strainer are clean. The propeller waste-pitched after launch as it was not allowing the engine to hit max revolutions. The prop shaft and related parts were all replaced at D/R recommendation.

It was a difficult and expensive installation, coming in about $5,000 over the original estimate. Part of the problem the twe learned after the installation commenced was that D/R could not install the stock Beta fiberglass exhaust, so a more conventional exhaust had to be fabricated at great expense. The other problem was that the old Merriman Yacht Specialties (MYS) steering pedestal throttle control lever could not connect to the Beta engine without extensive modification of the cable connections at the engine, which may still seem to be problematic and, possibly, unreliable.

The Derecktor/Robinhood mechanic is due to come here to Northeast Harbor tomorrow, 8/18, to again inspect the engine. We're very disappointed, as we've now lost two months of our summer sitting on the boat and waiting. Such is life, and our spirits are otherwise good.

So, our question for the expert mechanics among you, particularly other Beta Marine owners is: do you have any ideas about what is wrong with our engine? Have you had similar problems with your Beta engine, exhaust, or with the MYS shift and throttle connections? Any other ideas would be appreciated.

If any of you stop in Northeast, look us up. We're on float 306 near the Morris Yacht yard. PM if you want a phone number.

Thanks in advance and happy and safe sailing to all of you.

Jenn and Terry

Sea Hunt Video · Post by **Sea Hunt Video** » Aug 17th, '17, 09:59

Jenn and Terry:

I cannot offer much personal help. However, if you search on this board under "Beta dealer" you will find several CD owners who are associated with Beta Marine. "Ben Thomas" is a Beta Marine dealer (admittedly he is in Oregon but may still be able to offer advise). Also, as of July 2015 Jim Walsh has/had a cousin who was/is a Beta Marine dealer.

A Beta Marine dealer may be able to recommend a Beta Marine mechanic who truly knows these engines and is not a "rookie" with his first Beta installation.

There are several other CD owners with Beta Marine experience. For example, check out "Maine Sail". As most on this board know, he is an extremely knowledgeable mechanic, marine electrician, etc. Scroll down to his post on April 2015 at this thread:

http://www.capedory.org/board/viewtopic ... er#p183231

If I was in your situation, especially being in Maine, I would contact him and do whatever is necessary to get him to inspect your Cape Dory, the Beta engine, exhaust manifold, gearing, etc. I have never met him and have no business connection to him. However, I have read his website stuff for several years and his posts on this board. I think most (if not all) would agree that he is the truly an expert on this stuff with engines, electrical, etc.

Good luck

Jim Walsh · Post by **Jim Walsh** » Aug 17th, '17, 11:42

Try Joe DeMers http://www.soundmarinediesel.com/index.html. He has a reputation of going out of his way to be helpful....plus he's my cousin. He may have some advice that would be useful.

jen1722terry · Post by **jen1722terry** » Aug 17th, '17, 14:01

Thanks again, Jim and Roberto. Will follow your age advice.

Jenn and Terry.

Sea Hunt Video · Post by **Sea Hunt Video** » Aug 17th, '17, 14:39

jen1722terry wrote:Thanks again, Jim and Roberto. Will follow your age advice.

Jenn and Terry.

Jenn and Terry:

When you say "age advise" you are no doubt referring to Jim W.

He is indeed old. By comparison to Jim I am young.

Jim Walsh · Post by **Jim Walsh** » Aug 17th, '17, 16:54

Sea Hunt Video wrote:
jen1722terry wrote:Thanks again, Jim and Roberto. Will follow your age advice.

Jenn and Terry.
Jenn and Terry:

When you say "age advise" you are no doubt referring to Jim W. He is indeed old. By comparison to Jim I am young.

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