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Posts: 256
Location: plant earth | I have a 2005 Crestliner 1750 fish hawk with a mercury 75hp 4 stroke outboard. I think the motor is a little under powered I now think it should have been a 90 hp motor. It doesn't get on plane as fast and the top speed is a bit lower than I'd like. Is there a prop that I can put on to compensate for the difference weather it be a 4 blade and or a different pitch. I'm running the factory now. Thanks |
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Posts: 13688
Location: minocqua, wi. | find VMS Steve ... get prop'd correctly first before doing anything else.
that 75 and a 90 should be built on the same block. if you were to re-power i think you would spend a lot for a little. if you prop it correctly and still don't like what you end up with a trade out and into something different is more bang for your buck from this perspective.
good luck .. the right prop should make a difference. |
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Posts: 3486
Location: Elk River, Minnesota | Hiya,
Thanks sled, for the recommendation... 
First off, what kind of numbers are you seeing now? What we want to be looking for here is the prop's pitch and diameter, RPM's at wide open, and your speed (GPS if possible). All three of these pieces of information will help determine what direction to take for a different prop. Also, where is the motor mounted as it compares to the transom...one bolt hole up, two up, etc. That can play into how well the prop performs as well.
I believe the 75 has a max RPM of 6000 if memory serves me correctly and a gear ratio of 2.31:1, so propping the boat will be related to finding something that allows the 6000 rpms to be reached with a light load in the boat. The reason for this is so when you load down with other people and gear, you don't have to swap out props to match the load.
So...if you have an idea of what those numbers are, we can start from there. I'll help any way that I can.
Steve
Edited by VMS 3/7/2013 10:41 AM
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Posts: 256
Location: plant earth | About 5000 is max I've had it. And the GPS was back and forth from 34 to 37 mph at that 5000 mark. I've tried higher rpm but its seemed for the rpm there wasn't a big gain in speed so that why I was keeping it around that 5000 mark. I felt like it was just being abused then. Also that's 2 people and minimal gear and about a 1/2 tank of fuel.
Edited by jdeezay74 3/7/2013 11:25 AM
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Posts: 3486
Location: Elk River, Minnesota | Hiya,
From what it sounds, the prop is letting loose, which means you will gain rpms fairly quickly, but not gain any speed. With that set up, I doubt you would see any porpoising. What pitch and diameter prop are you running?
Thanks
Steve |
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Posts: 256
Location: plant earth | I dont know and tried to find the factory specs but cant all i can tell you is that its the OEM mercury one for what thats worth. not much help on this subject. |
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Posts: 256
Location: Valpo IN | Look on the prop the #`s should be stamped on it. good luck - Steve will get you straight |
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Posts: 256
Location: plant earth | ok i have finally had the chance to get the boat out of storage and get it ready for some walleye action. i looked on the prop and it is a 17 pitch i would assume thats the 17p on it? and 13 1/4 x 17. is there an option for a better hole shot and some better top end? 3 blade 4 blade. is it worth the $$$$$. THANKS
Edited by jdeezay74 3/30/2013 2:22 PM
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Posts: 1184
Location: Iowa Great Lakes | Dropping to a 15 will help alot and may not loose much on top end..... Go SS if possible... |
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Posts: 3486
Location: Elk River, Minnesota | Hi again,
Now that you have the boat out, can you take it out for a spin with just you and a light load of gear? The goal being to take it to your full wide open throttle and trim it up to get the numbers, (speed, rpm). Then, trim it down some and make some moderate turns to see if the prop will hold the water. With an aluminum prop, it usually will not hold in a moderate turn unless it is trimmed down fully.
If a prop change is needed, it will always be a compromise of some sort. In most cases, to gain hole-shot, you loose speed and vice versa. The only way to gain in both areas is to have a prop that is steel and vented, but at your HP, you may not find a significant enough increase to warrant the $$ you would need to spend. BUT...a good vented steel prop usually allows a higher motor height off the transom, the blades are thinner and hold water better, which means less trimming.
I'm hoping you can get some solid numbers, and don't be afraid to take the motor all the way to 6000 or higher if it can do so. The motor is designed to go to 6000 for safe use, and can handle higher rpms for short periods of time for testing purposes. This will determine what can be done for a prop change.
Steve |
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Posts: 43
| I have a 1650 fish hawk with a 60 hp mercury 4 stroke. I purchased it new at the begining of last year and played the prop game for awile. Went down 1 pitch and went to a 4 blade prop to get hole shot and max speed (35 mph) out of it from the factory prop. tried 4 different ones. Was having a problem getting up on plane with 3 guys in boat. Works great now!
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Posts: 1091
Location: Hayward, WI | Try a 15 pitch Splitfire 4 blade aluminum by Mercury. It is designed exactly for a boat like yours. |
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Posts: 256
Location: plant earth | Ok I hit the open water at the 6000 rpm mark GPS was reading a solid 39 mph. On the turns it definitely loses its bite in the water and rpms rev up. It does the same thing on a hole shot if I gas it up to about 3/4 throttle. It loses its bite just as I get on plane. But if done in moderation it never does it. |
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Posts: 3486
Location: Elk River, Minnesota | Those are actually some good numbers there!!
Here is what I think you can do... If you go onto ebay, find a 17 pitch michigan ballistic prop. Should be 15 spline and I believe 13-5/8" in diameter.
Once you have it, get it on and take the boat out for a spin. It will hop up on plane better and should hold the turns much better as well. Where you will see a drop is in your overall RPM's...probably around 300 or so from where you are at now. THAT will be solved by moving the motor up off the transom 2 more bolt holes. This could potentially put you at the highest motor setting, which should still do well. This prop is designed to be very aggresive, as it has thinner blades and substantial cup on the tip and trailing edge. I had one on my 90 yamaha 2 stroke and it performed extremely well. With this prop, I would bet you will see both an increase in hole shot and an increase in overall speed...especially if you raise the motor up a hole or two.
The 17 pitch ballistic will act more along the lines of an 18 pitch prop, but in my experience, I found it turned the same rpms as my stock aluminum....so I only gained with it.
The other option is to find a solas 3 blade aluminum, which will be cupped more than your stock aluminum, and it will be cast thinner as well. This is due to their process of what they refer to as "squeeze casting", which instead of just sending melted aluminum into a cast, they literally push it in there to remove the porous nature of aluminum, allowing for thinner blades and a more aggresive fin design. The prop acts more like steel, with the forgiveness of aluminum.
I feel in your situation, the steel could do you well. One note, though...not every prop works well with certain combinations, so you may find that both of the props I have mentioned here may or may not work...but the fun is trying them out!! If you can find someone who would let you borrow a prop, that would at least save you the $$ to try one out as well.
Ebay has good deals on used stainless...I've purchased many off of there and if the prop doesn't work for me, I am usually only out the cost of shipping as I can sell it for the price I purchased (in most cases).
Steve |
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Posts: 256
Location: plant earth | Thanks Steve ill doing some looking on eBay and see what I come up with. One more question if I get a prop that is more efficient at moving the boat in the water will it be more fuel efficient on the motor. Better proformance and fuel economy that's a win win.
Edited by jdeezay74 4/3/2013 2:00 PM
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Posts: 422
| Jdeez, I agree those actually aren't bad numbers for your set up. You are certainly underpowered, but I think you are getting what you can out of that set up. You can spend a bunch of money to switch things up but those really sound like realistic numbers for that set up. You're only real option for increasing hole shot and top end is a different motor. For comparison, I have an 1850 Fishhawk with a 140 Suzuki and my average top end with two guys and gear is only in the mid forties. I had a lot of work done with props to get the optimum rpm levels. Good luck....
Craig |
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Posts: 3486
Location: Elk River, Minnesota | Hiya,
One word for you: Absolutely!!
By no means is an outboard very efficient regardless if it is a 2 stroke or 4 stroke due to the amount of drag created by trying to move a 2500 pound boat through water. But...anytime you can get more boat out of the water, you increase the efficiency of the motor. The steel prop will lift the entire boat more, and moving the motor up helps that as well, as long as less lower unit in the water. I think this will be a good move for you. Might be able to break 40mph with the boat, although if you don't, those numbers are definitely nothing to be mad at. You will gain handling as well with a prop change.
Good luck and keep us posted!!
Steve |
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Prop upgrade question?