Prop and Speed Question

[Qualityman691]

I just recently purchased a 1995 35.5. The boat has a 3 blade prop (I an not sure of the size or pitch). When crusing under power I find the max RPM is about 3200, which seems low to me. My speed at 2800 RPM is around 5 knots. I had the bottom scrapped and cleaned during the survey so I am sure the bottom is in good shape. The engine runs fine and does not smoke. The engine is the Yanmar 3GM, 30 hp.

I am wondering if anyone has any ideas why I am not getting more RPM's and/or why I might not be able to get any more speed.

Thanks for your help.

 

[Honeyman]

Pretty sure 3400-3600 is max rating for your Yanmar, its on a plate on the engine with serial number. I have same boat (94) and it will make approx. 6-6 1/2 kts at 2800-2900 which is upper end of the "sweet spot" for me. 3 blade fixed, 16X11X1 right hand is what I replaced the stock 2 blade prop with. 16X13X1-2 blade was original on mine.

 

[Les]

I also had a '94 Hunter 35.5 with that same engine. I used a two blade standard prop and did about the same as Honeyman reported. About six and a half knots at about 3000 rpm. Over the years on a number of my boats I've had either a two or three blade prop. I've not found that the three blade is faster; only smoother and it will help you get through chop and rough water better--a little more drive. The two blade is good for racing. The next step up is to get a folding or feathering prop. That will allow you to sail faster but it won't help your boat speed.

One other thing to check is your boat speed display against your GPS. Perhaps yours is not properly calibrated.

 

[Alan]

In flat calm water my boat maxes out at 7.2 kts and 3400 rpm. At 2800 rpm, which is my usual cruising speed, the boat will do 6.8 kts. I have a 2 blade MaxProp

If your speed readings are correct engine is running OK and the bottom is clean then you probably have the wrong prop.

 

[Steve Dion]

The max rpm is also controlled by the engine govenor. Assuming that it is set for 3600+/- you would need to assume that your prop may be over-pitched (not uncommon).

If you opt for a new three bladed prop, I would recommend that you look at a Campbell Sailor Prop. They are about $600 and worth it. Your next step is a folding/ feathering prop, but they start at over $1,000 and require maintenance.\

I suggest that you find out what sized prop you have and contact a "good" prop shop and find out what should be on your vessel. They will need to know the engine/transmission and a few other measurements in order to give you a good estimate of what can be done.

 

[Qualityman691]

Thanks for everyone's input. I suspected it could be an incorect prop, but I am no expert in that area and wanted some additional input. There is a pretty good prop shop in Cape Coral. I will get in the water and take some measurements this weekend and give them a call.

 

[Steve Dion]

If you are going to get in the water, be sure to get a measurement on the distance from the middle of the shaft to the hull. I am not sure how they would like you measure this, but it is one critical measurements.

 

[Qualityman691]

Thanks Steve. I had read last night to make sure to have that measurement from the shaft to the hull. I have a guy who does my bottom cleaning. I am going to see if he can pull the prop and I can take it, along with all the key measurements and specs, to the shop.