Prop selection

[mistaredone]

I replaced my 93 2 stroke 90hp Mec this year with a 2000 90hp 2 stroke Mec after getting my motor stolen last fall. My old motor would do 50 mph trimmed and the new motor only 38 mph. I tried going on a few sites to find the right prop but never got anywhere. Hope someone can help

 

Specs

 

2000 2 stroke Merc 305 lbs 5500 rpm max

93 cobra bass boat 16' mod V fiber glass

50 L of gas on board

200lbs of equipment

3 guys on board 500lbs

 

trimmed we hit 38 mph at 3800 rpms

 

Also I was hoping to save some cash buying used. Any advise on buying a used prop or am I better off buying new?

[vance]

Your RPMs a wide open throttle should be between 5300-5500 or you risk over heating your motor.To me you have too much pitch and I know there is a formula for figuring this out but I don't know it.

 

vance

[POLLIWOGG]

Your motor makes 90hp at 5500rpm but at 3800rpm it makes far less than 90hp so you have to get that rpm up by dropping pitch or diameter of the prop. I think it goes an inch of pitch is roughly 400 rpm and an inch of diameter is 200 rpm. The smaller prop will give you a better sense of range between slow and wot.

[workwear]

you might wanna give louie a call at city wide welding he has an array of props and might even help you with the pitch of it...located in missisauga near the airport.has helped me with a few props

phone number is 905-770-0316

[Terry]

what size and pitch of prop

you should have something like this

size

13.500pitch24.0

 

 

 

 

try this prop selector site

 

http://sites.mercurymarine.com/portal/page?_pageid=126,53050,126_53052&_dad=portal&_schema=PORTAL

[corvette1]

what size do you have now 5500 then 3800 now it would be a lot of overpitched to lose that much rpm some thing else could be wrong with the motor i went down from a 21 p to a 19 and gained only 400 rpm

[ecmilley]

couldn't see the factory prop being that far off, are you sure everything else is ok, fuel pick ups, filter ect.

is there any other issues like hole shot ect.

[bigbuck]

Another thing to look at is your motor, is it mounted on the right holes?? If the motor height is incorrect, it will throw things off too. What pitch was the prop you were using?? You are definitely off there. What about asking the guys who installed the motor for you. 3800rpm should be around your cruising rpm, not full throttle.

[walleyemen]

Prop to pad should be between 2.5 and 3 inches, boat level and engine trimed the same, you could be to high or low, i'm, messing with props as well, 48 mph at 4300 rmps.

Check this out or search the site ,someone should be able to help you!

http://www.bbcboards.net/zerothread?id=65514

http://www.bbcboards.net/zeroforum?id=49

Edited June 16, 2010 by waynechute

[mistaredone]

Yast year the boat would kick right up on the hole shot but in the spring I put a new 75lb trust Motor Guide trolling motor and 2 12v battaries up on the bow. I figured this would make for a better hole shot. Now she planes with no problem but not what I expected.

 

I guess im best off going back and buying a new prop from the same marina that did the work in case I need to try a few pitches.

 

 

Thanks for all the help.

[DRIFTER_016]

My 90 horse on my 18' aluminum fisher is a 13X19 and the motor tops out at 5300 rpm.

Weight of the boat wet is about 1000#'s. That is without occupants.

[mbac31]

I once had a smaller bass boat with a 90 horse. Factory settings the boat ran 45mph tops. When I ws done that summer I was getting 62,5mph WOT. Takes a while to find a sweet spot for any boat/motor combo. I'm working on my other one now and gaining with every new prop. Costlt though to buy new. Try buying used no matter what. Lots of places online to find them. Weight configuration in your boat will play a huge part in speed. I would not leave batteries up front. Will be hard to trim up with extra weight. I would place them in the back and wire them up that way. Your motor may be t low but it sounds like your prop. With batteries up front and gear the boat is bogging and pushing to uch water. Lots of variables. Get the weight out of the front first and start playing with props.

[RudeBuoy]

Are you running a Bayliner Cobra or a Viper Cobra hull?

[Billy Bob]

Mercs suck,

 

Get a 90 hp ETECH motor...

 

Problem solved..

 

Seriously, hope you find your answer and report back

 

Bob

Edited June 18, 2010 by Billy Bob

[brufan]

Mercs suck,

 

Get a 90 hp ETECH motor...

 

Problem solved..

 

Seriously, hope you find your answer and report back

 

Bob

 

I just bought a 90hp etec and have the same problem. Luckily there is a Piranha prop demo going on at a local Ottawa tackle shop tomorrow morning and I will be looking to replace the standard 13.25X19 prop that came with the etec. This way I can try different pitch props before buying anything. Right now I can get 44mph but am only at 4300rpm wot. So basically it doesn't matter if it's a merc or an etec, the standard props suck.

brufan

[Terry]

are you guys getting your MPH by a speedometer or from GPS or radar gun....

 

I have trouble with some of the speeds stated here

 

 

a prop can only go as fast as the math allows

 

which means rpm times pitch

 

there are charts that show top speeds of many makes of props

[brufan]

are you guys getting your MPH by a speedometer or from GPS or radar gun....

 

I have trouble with some of the speeds stated here

 

 

a prop can only go as fast as the math allows

 

which means rpm times pitch

 

there are charts that show top speeds of many makes of props

 

I'm getting my speed from the speedo (two weeks old) but regardless, I'm just saying my wot is only 4300rpm and need to try different props.

[Terry]

yeah it wasn't yours I was wondering about

 

but speedometers are never accurate at all speeds and the math didn't seem to add up with some of the other claims..I don't doubt them , so I would think their speedometers are off. GPS is a very accurate way to test

 

you do need to find a prop that will get you near the top rpms for your motor

[charlesn]

Yast year the boat would kick right up on the hole shot but in the spring I put a new 75lb trust Motor Guide trolling motor and 2 12v battaries up on the bow.

 

The batteries up front will definitely cost you some speed. You want them as far back as you can get em. That's like a 100+ lbs weighing down the nose of your rig.

 

When I had a boat similar to yours powered by a 90 - I found a Ballistic prop to be the best. The 22". I was lucky and had a mechanic that let me try four or five different props until I found the right one. If you have a marina or place that you deal with regularly - ask to try a few. If you take them to the ramp and test them you will find a huge range of difference between props.

 

I'd start first though by moving the batteries to the back and see how much that helps.

 

3800 rpms is way too low for WOT.

 

Good luck,

Charles

[mbac31]

All mine were done with GPS and also Smartcraft guages. I now have it connected to my Lowrance HDS on front and Back as well. The speedo's on boats suck, the digital Smartcraft are very good but costly. . Takes alot of time to figure out how your boat runs. I have three props for different situations. One for Just me fishing with normal load. One for crusiin and water sports and ne for Tournaments Loads and hole shot. Took me a long time to get it there but works fine for me. 2 of my props have been blueprinted and worked to achive this and I will leave the dollar amount alone as some will figure I have issues.

Edited June 18, 2010 by smalliefisher