What Pitch prop Crazy

[Ed T]

Hi its a me. Sorry to bother. Here is problem I have a 1990 90hp 3cylinder mecury outboard. on a 19'ft cuddy cabin bayliner. Had it out a few weeks ago and ran it with a 13 1/2 x 17p Prop. At wot speed was 28 to 29mph. and rpm was 5500 at that speed. Now the other day I switch props and ran a 13x19p prop at 31 to 33mph at 4500 to 4600 rpm. What size prop do I need to get it in the rpm range of 5000 to 5500 for that motor and still retain my speed at 30 to 32mph. Thank You. Ed PS I also have a 13x17p prop which haven't tryed yet

 

[jestor68]

Re: What Pitch prop Crazy

The 17 is running right at the top of your rpm range(good). The 19 is running at the bottom end of your rpm range(not so good).

What you need is something in the middle. Guess what; Mercury makes a Quicksilver Silverado (SS) 13X18 that should drop your rpm from 5500 to 5300 and gain you a couple mph.

 

[Ed T]

Re: What Pitch prop Crazy

Thanks Jestor68. I have a few props for the motor. But there 13x17p. What I may do is bring them in and repitch to 18p. May be cheaper. I had a SS on it before that motor didn't like it at all. Real poor mph and rpm. Thank You So much. Ed

 

[jestor68]

Re: What Pitch prop Crazy

I used to have the same boat, except mine came with a 125 Force motor. It used a 19 pitch prop and gave overall good performance. It was the right prop for that particular boat. As I recall, it did around 39-40 mph.

Your boat has a 90, which might be considered under powered. As your own test indicates; it runs great(5500) with a 17pitch. It bogs down with the 19, but gets a couple mph more top end, when it finally gets wound up. Put a couple more folks in the boat, and it'll likely fall on it's face(with the 19).

The reality of your situation is that your 90 hp motor is doing all it can do on that particular boat. You will likely need to stick with a 17 pitch prop for good all around performance. The "right" SS prop (of the same size ) will usually perform better and gain 1-2 mph. You have to decide whether the cost of SS versus aluminum is worth the slight advantage.

Sometimes the brand of prop makes a difference. Contrary to popular belief, they are not all created equal.