Prop for a hunter 25.5

[sailorkoop]

I'm about to purchase a 1986 hunter 25.5 with a Yanmar diesel. The current owner said because of the 2 bladed prop there is a vibration in the cockpit when running the engine. My questions are: why is the prop only two blades? Can i put a 3 bladed prop on the boat and will this stop the vibration? What will be the effect? Is the vibration normal on a hunter 25.5?

Thanks for your help........I'm new to sailing but learning and reading all i can.

 

[DougM]

Changing from a 2 blade to a 3 blade prop will smooth out the vibration somewhat, or at least move it to a different frequency range. The basic reasons for a 2 blade prop on a sailboat are: its cheaper, and it creates a little bit less drag when sailing.

There is no problem, other than cost, in fitting a 3 blade prop or a feathering/folding prop as long as there is room between the end of the prop shaft and the rudder.

 

[sailorkoop]

thanks Doug........Manistee!..won't be long you'll be back in the boat!..Have a good summer!

 

[Steve Dion]

There is no guarantee that this is the problem. 2 bladed props are more prone to vibration than 3 bladed. You really should get the drive train checked out before you spash her. Otherwise you may be paying for another pull/splash.

 

[sailorkoop]

good idea...thanks. Would anyone have idea what a 3 bladed prop costs?

 

[txtowman]

$25-$3000 depending on a lot of things.

 

[Ross]

A prop that is not straight will vibrate. One blade can be pitched for 9 inches and the other for 9.5. It could have be bumped at sometime. I bought a used 3 blade for 75 dollars and had it repitched and serviced for 125 . I ran it for a couple of years before I had it worked on and the difference was nothing short of wonderful.

 

[sailorkoop]

$25-$3000 depending on a lot of things.

lol...thanks, you've been a lot of help!...I bet you always are!

 

[rardiH36]

Engine Itself Also Vibration Source - Maybe Nothing is Wrong

Something else to consider about vibration that I didn't see mentioned yet. Besides the prop and condition of the drive train, the engine itself can be a major source of vibration. I looked up the Hunter 25.5 on yachtworld.com saw an offering listed as having a one cylinder Yanmar. One cylinder and even a two cylinder diesel engines can vibrate very noticeably. Just their nature. The ~1979 made two cylinder Yanmar 2QM20 on my boat can cause my anchor to start resonating against the anchor roller fitting at certain rpms even in neutral without the prop turning. (It has a nice bell-like tone though.) When motoring, the trick is to learn the rpm ranges where the vibrations tend to cancel out. For example the smoothest spots on my boat are 1600 rpm (= about 3.5-4.0 kts) and 2200 rpm (= about 5-5.5 kts). If the motor mounts are getting worn and no longer provide adequate support and vibration dampening, that can also be a cause for increased vibrations.

From my Seloc repair manual:

"Smaller engines with 1, 2, or 3 cylinders will often vibrate violently at slower rpm. This is particularly noticeable with lighter engines whose softer mounts are optimized for the smoothest running at operating rpm. All engines have rpm bands where the vibration is greater. Often the vibration is more pronounced because of poor installation."

 

[sailorkoop]

Makes a lot of sense. thanks for your help all! I've also discovered a chainplate leak but i guess thats common on the Hunter 25.5.......Looks to me like you'd have to cut a hole in the boat to get it fixed!!!

 

[Steve Dion]

Sailor: Check out a Campbell Sailor Prop. This is probably one of the best fixed props on the market. The will run about $600 (maybe less) but it will probably be the last prop you will ever need. They look like you could hit a log with them and it would not even fase it. They also have much better sailing charastics than your traditional Michigan Sailor props.

 

[Prime Time]

I don't buy it!

I drive a Hunter 25.5 on Weds. night racing at our club for years. We have a 2 blade martec with a Yanmar 1 GM engine. Our drive train is as smooth as butter. No vibration and little sound compared to many other boats that I have sailed.

It is not the fact that you have a 2 bladed prop.