New prop..new problem, Help

[Doug B]

As I wrote the other day we have added and been happy with the performance of a new Campbell sailor 3 blade prop. Now the problem. We can get about 6 kts. out of 2,500 rpm. We rather run around 2,800 rmp and get closer to 7 kt. When we run for long period of time at 2,800 (especially heavily loaded, pulling dingy, going against tidal current) we get our overheat buzzer. If we back down to 2,000 it shuts off in less than 3 minutes. When not heavily loaded and in slack tide, max rpm in forward gear is 3,200-3,300. I was under the impression that that was high enough to assume we were not overpropped. We have checked the mixing elbow (clear) and breather and have new fuel in the tank. We have not cleaned the header (heat exchanger)tank yet but believe it to be clear too. We never had this problem with the stock two blade. Any advise? Should we worry or just run at 2,500 rpms (which we can do all day long with no buzzer...even against a tide)? We are so please with the props smoothness, lack of drag under sail and speed under power, I hate to take it off.Doug

 

[Alex]

If all is clean and cleared..

..you are probably overproped ,and straining your engine.As per boat size , I think 6.5-7 kts its a fine cruising -or even max -speed for that boat equiped with Yanmar 3GM.But you should be doing it at a higher RPM -about 3200-3300- to fully benefit the engine potential and keep it 'healthy'.

 

[Jim McCue]

over heatin'

Is your dingy a Zodiac/rubber type? If so, why not "hang" it on your transom and see if you get the knts without overheating.Jim McCue

 

[Steve Dion]

Just slightly overpropped.

Doug:You should contact Campbell about this. I would think that if you had them take 1 degree of pitch out of the prop you will probably be OK. One degree of pitch will probably give you another 200-300 rpms.I cannot remember which engine you have but the 2GM/3GM 20F's should be able to rev to 3600 at WOT (wide open throttle). If you cannot get these revs then you may be slightly over propped. Obviously these props have some different characterics and they should be easily overcome with a little adjustment. Remember that the general rule on the RPM's is that you should be running between 70-80% of the max rating on your engine so the 2500rpms is within the acceptable range.