Communication from Gerry Douglas regarding propellers.

[jnnielsen]

The following address the prop/ cavitation issue on the 350. Would you please make this available on the web and in the MAINSHEET? Please contact me should you have questions.

There have been some owners concerned about noise and or vibration from the prop. The degree of the noise/vibrating seems to vary greatly from boat to boat and owner to owner because this is a very subjective issue and not measurable in any practical way.

It is my experience that every boat will experience cavitation at certain times. Simply stated this occurs when the propeller blade speed through the water exceeds the speed of the water flow over the blade surface leaving negative space behind the blade that is filled with oxygen pulled out of the water, when the flow "catches up" with blade speed the cavitaion stops. (This is an over simplification of a technical explanation, but basically correct ).

The conditions that can create cavitation are typically when the boats speed through the water is temporarily slowed by a head sea or when rapidly accelerating and continues until the boat speed through the water catches up with the prop speed.

There are ways to minimize the cavitation noise/vibration, one is to use a smaller diameter prop ( this would be much less efficient ) another is to slow the prop speed, ( this would require a much larger prop to achieve hull speed ) . The most practical is to decrease diameter to reduce tip speed and increase blade area to compensate for the diameter reduction and improve flow characteristics over the blade .

The props originally fitted to the 350 were 15" diameter 9" pitch 3 blades , a good compromise as is every sailboat prop ,where minimum drag under sail and efficiency under power are balanced.

In order to address the concerns of 350 owners about momentary cavitation we solicited the help of several 350 owners, on both coasts ,to do parallel testing of alternate prop designs. Three different designs were tested , during the test period Michigan Wheel, Catalina's prop supplier, introduced a new style prop designated the "M" series . Tests proved that the "M" series prop combined the best performance under power with minimum cavitation . The "M" series has a wider blade , therefore more frontal area than a traditional sailor prop and will produce slightly more drag under sail ,( all sailboat props are a compromise ), so racers or light air sailors may choose to stay with the original factory supplied prop.

Catalina will make the new "M" series props available to 350 owners , who wish to change props at our cost of $195.00 plus shipping. There are a limited number of props available at any one time , so we may not be able to fill all orders at once . The props will be shipped from the Largo Florida Plant and can be ordered Customer Service in Largo or though the Parts Department in Woodland Hills Ca.

Catalina has started installing the new Michigan Wheel "M" series Sailor props on hull number 400 and higher as standard.

Thank you , to the 350 owners on both coast who participated in the prop testing program.

Good Sailing, Gerry Douglas

[Richard Collins]

I am pleased to report that after replacement of the orignal 3 blade prop this morning with the new 3 blade prop obtained from Catalina, no cavitation at all over the full rpm range. We also did not experience cavitation when accelerating rapidly. This is a huge improvement for us.

Also, the 35 boat reported no cavitation as well after installation of the new prop even when motoring into a stiff chop.

Richard
s/v Eagle's Wings C350 #37

[LONGHAWK]

Wow, the new prop is a huge improvement. I too changed (hull #173). No cavitation and noticeably different / smoother than the previous three blade. I found that the new prop had a three inch throat instead of the original prop's 2 3/4 inches. This covered the hole where the locking / safety cotter pin would go, but luckily my shaft actually had two holes drilled. We used the aftermost hole and all was fine. I called Michigan Wheel with Warren Pandy's help and the chap at Michigan Wheel indicated that the corecct dimension shoould have been 2 3/4. I did the prop change out of the water. If you do it in the water this would have been a bear to sort out.
Sam
LONGHAWK #173

[Chips Ahoy!]

I received the new prop today.

It's a Michigan 14R10 M371224. Is this the correct replacement?

I had it in my head tha the replacement was going to be a 15R9 with fatter blades.

-george

[LONGHAWK]

the new prop is a 14*10. This supports the theory that the blade tip to hull clearance on the 15inch prop was marginal. I actually have piiting on the blade tip that to my eye would have been caused by cavitation.
Sam
LONGHAWK #173

[Last Boat]

I replaced my old prop with the new recommended prop this weekend and I also received a new bottom job. All of this has increased my speed at cruise RPM by about 1 knot. I am pleased with this improvement, but I now am experiencing a high pitched whine in the 1100 to 1600 RPM range. This whine wasn't noticed on my initial throtle up and exit of the fairway (about 30 minutes in this range). I had completed the trip back to my dock (about 5 hours at 2400 RPM) before I noticed this. My question, has anyone else noticed this with their new prop?
Nelson Gainey
Last Boat
C350 #345

[BobWintemberg]

We have 2003 hull #77. If one wanted to use a fixed 2 blade prop to minimize sailing drag, but utilize the most efficient 2 blade for the boat, does anyone know what that prop diameter and pitch would be?