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95 115 mariner new prop needed fear current is too pitchy

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fazsha1

New member
"Recently picked up whats turn

"Recently picked up whats turning out to be a swiss-army knife of mid-sized boats. 95 19' Alum Spectrum Bowrider. Does everything from chasing small moths, Wakeboarding, to chasing Tuna 15 miles out.

Currently being pushed by a 95 115 Mariner turning a standard Alum3Blade, "48 77348 A45 21P". It's been dinged often and so I've ground it to keep it reasonably balanced.

Current perf is WOT = 35mph @ 4500. Worried I can't make a good choice due to damaged current prop. Also worried why engine isn't over RPM'ing. Two choices: 1) current prop is too pitchy (even damaged). The foam filling is soaked; adding mucho weight to boat (heck, gives a great ride in 3 - 4' chop though


So... should I... get current prop rebuilt and retest; go from there? Should I weight the boat and try to find the original dry weight, and go from there?

Any advice is greatly appreciated as this is alway s a bit of artsie-science.

Glen"
 
"Glen, ran some numbers throug

"Glen, ran some numbers through the calculator and at first glance your set-up should be running a 21 pitch and getting into the 5200 rpm range and getting you a touch over the 40 mph mark.

Unless, as you possibly suspect, that you are pushing alot more weight than you (or I) figure.

Used some specs from NADA to determine your total displacement at about 2200 lbs, which would include 2 passengers.

If you trailer your boat it should be fairly easy to find a weigh scale somewhere that could give you a good idea of what it actually weighs - even if you include the trailer weight which would equate to a good passenger load with related "junk" for the day.

As a rough rule on your set-up, you would be looking for 2" less pitch for every 400 pounds above the 2200 which I used for the calculations.

Of course a tach is always the best way to prop a boat, but this should give you a decent starting point....."
 
"Hi Graham, thanks so much. Am

"Hi Graham, thanks so much. Am I reading into your first thought that I should rebuild the carbs (to have an honest shot at 5200); or should I rebuild the prop to new spec and retest? Both?

I can weight the boat easy enough... but damn... I've tried every kind of search (except for the right one); and not been able to find the spec'd weight of the boat.

Thanks again."
 
"Glen I wouldn't say the c

"Glen I wouldn't say the carbs have a problem at this point, sounds alot more like a simple "set-up" problem - prop too big, more weight than you thought etc.

I (think) the dry weight of your boat should be about 1300 (rigged/no gas - NADA numbers for 19' Spectrum) - add 300 for the motor, a bit for gas, battery and safety gear and I figured that 1800-1900 should be your "passengerless" (is that a word?)
displacement weight of the boat.

Personally, I would have the prop redone first - and ask them to change the pitch down to 19. In any case, the 21 is too much for your rig and simply dropping it to a 19 should bring your rpms up by 400-500 (close to your proper WOT range)...."
 
"Glenn, If you have ground do

"Glenn, If you have ground down your prop, you may have seriously changed its characteristics. I would be in the market for a new prop. Remember grinding 1/3 of the blades off a prop makes it a test wheel, with very little thrust, but plenty of engine load.

I am currently running a Merc 135 HP V6 on my 600 pound 16' speedboat. I have a 21" pitch Rapture, which I can spin up to 5500RPM, with max trim. I therefore think the 21P prop is too much for your setup. I think a 19P prop should be better. You might even like a 17P prop, so see if you can buy a 19P and try it and exchange it if necessary."
 
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