Prop selection

[robsnot]

Hi, guys. I am sorry to post such a newbie question, but I am a boating/boat owning newbie.<br /><br />I am the proud owner of a 30 year old Newport 16, a 15ft 7in long, 6ft wide sailboat. I purchased a used 1978 Evinrude 2hp outboard to power it. The completely loaded boat weighs about 1100lbs, then add 400-500lbs for crew. My max hull speed should be just under 5kts (13ft 6in LWL). I plan on sailing in a saltwater bay as well as lake sailing. When using the outboard, I can go about 3.5kts, but the motor doesn’t sound like it is running at full throttle – the RPMs seem low compared to when I run it in a bucket. <br /><br />The outboard has a 3 blade prop and one of the blades has a significant nick in it, so I’d like to replace it – but there are so many props and choices, I’d like a little help.

 

[CFronzek]

Re: Prop selection

Robsnot,<br />Your motor is working hard to move a lot of weight and a nick in the prop should not slow you unless there is some additional damage. <br />Since this is a used motor a cylinder pressure check will give you an approximate idea of how much wear and tear this motor has suffered over the years. As cylinder pressures fall so does power. Cylinder pressures below a hundred pounds indicate that the motor is a bit past it's prime. The motor may continue to run for many years but it will have to work harder to move a given load. <br />One thing you should consider is whether or not this motor is large enough and/or powerful enough to allow you to make headway when there are adverse winds and seas. Trying to outrun a storm at less than 2 knots could ruin a day on the water. <br />Charlie

 

[WillyBWright]

Re: Prop selection

To get the most out of that motor, you'd want to get a prop with as little pitch as possible. That'll get the RPMs up to where the motor is actually producing all of that two whopping horsepower. Propellers are measured as diameter x pitch. Look for the lowest pitch available for that motor. I don't have a chart, but I kinda think that motor only has one option. So you might be stuck with what you have. But it sure beats paddling! Only drawback is that you have to register your boat as a motorboat and have a fire extinguisher on board. Motorboat registration costs more, at least in my state. Not that a few bucks is a big deal.<br /><br />One thing I noticed on mine was that if the wind was slight to dead, the boat would move faster with the motor if I left the sail up than with the motor alone. Significantly! I figured the sail would slow me down or go slack, but I was wrong.

 

[robsnot]

Re: Prop selection

When I w2as considering buying a motor, I thought about the wind. Then I remembered "Its for a sailboat!" If I have wind, I have power. If the wind is blowing the wrong way, I need to become a better sailor. <br /><br />Current is another issue, but a small motor is a small motor. <br /><br />Can anyone tell me what the WOT is supposed to0 be on a 1978 2hp Evinrude? That seems to be the crucial bit missing in my search for the correct prop.<br /><br />As to nicks and suchy, my Seloc manual says any significant nick in prop will cause wobbles and that can cause the engine to wear prematurely. Since I need to replace it, I figured I might as well try to optimize the prop selection.

 

[petrolhead]

Re: Prop selection

My little British Seagull will push a boat way bigger than you might expect for its 2.5hp, that's because of the very fine pitch 4 blade prop it uses, British Seagull called them "fans" rather than propellers!<br />It will never push anything very fast, but it'll push my father-in-laws 23' cabin cruiser at 4 knots, the same speed that it pushes my 9' dinghy!

 

[jimmbo]

Re: Prop selection

4200 to 4800 rpm is what is stated for the 2hp in the 1978 catalog.