Need prop advice Honda BF15 on 14’ aluminum boat, poor performance at 3200 ft Altitude

slief

Registered Lurker
Jun 8, 2007
507
12
Whitefish, Montana
Name
Scott
Boat
14’ Crestliner Sportsman
I have a 2003 Crestliner 14’ aluminum boat with built in decks. The boat is kind of on the heavy side for the existing motor. The boat likely weighs around 1500-2000 pounds dry. It’s fitted with a 2003 Honda BF15 4 stroke. I recently moved from So. Cal to Montana and noticed that the boats performance is terrible. I am at around 3200’ altitude. The engine was making around 3800 RPM at full throttle according to a digital tach and a top speed of around 8 mph with 3 people on board including myself. I checked the throttle stop and it’s going to full throttle. I just swapped the original 102 main jet for a 100 sized main jet which brought the RPM up to around 4000 RPM with 4 on board and more then likely around 4200-4400 rpm with 3 on board (I haven’t tested it with 3 yet). The max rpm should be between 4500-5500 rpm and the motor should make 15 HP at 5000 rpm (sea level). I will also note that the cavitation plate is about level with the keel and there is no simple way to raise the engine as it is clamped on. I could raise it an inch with a spacer or drill the hull but I’d prefer not to do that unless the benefits will warrant it.

I could swap the new 100 main jet to a 98 but that may be too lean for my present altitude and many of the lakes I fish. I’m thinking I need to get a new prop and really not sure what to go with. The boat currently has the original 4 blade 9.25 x 10” prop. As it sits now, it doesn’t get up on a plane. I know the motor is undersized for the weight and boat but I’ve had this boat for 15 years and really don’t want to buy a new motor due to cost and the fact that this motor runs great other then not making full rpm. I use this boat for fishing and my goal is obviously more speed/better top end.

Any advice would be greatly appreciated.

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dwaynesda

dwayne
Apr 27, 2003
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II would get rid of the 4 blade prop. It is not necessary for a light weight boat. Get a 3 bladed 9.25 x 8 and you should be able to get the rpms you need.

I think the 4 bladed prop is your main problem. The more metal in the water, the more friction and it will turn slower.
 
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slief

Registered Lurker
Jun 8, 2007
507
12
Whitefish, Montana
Name
Scott
Boat
14’ Crestliner Sportsman
II would get rid of the 4 blade prop. It is not necessary for a light weight boat. Get a 3 bladed 9.25 x 8 and you should be able to get the rpms you need.

I think the 4 bladed prop is your main problem. The more metal in the water, the more friction and it will turn slower.
Thank you very much for the advice. Do you think that will add much to my top end speed? It sure would be nice to get across some of our bigger lakes faster!
 
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slief

Registered Lurker
Jun 8, 2007
507
12
Whitefish, Montana
Name
Scott
Boat
14’ Crestliner Sportsman
I would get rid of the 4 blade prop. It is not necessary for a light weight boat. Get a 3 bladed 9.25 x 8 and you should be able to get the rpms you need.

I think the 4 bladed prop is your main problem. The more metal in the water, the more friction and it will turn slower.
Interesting. I just checked the Solas Prop website. Their prop finder also suggested a 3 blade prop. Their suggested a 9.25 x 7” but their prop finder does factor in existing RPM. Only estimated boat weight and elevation. What impact would a 7” pitch vs 8” pitch have on overall performance? I would guess that 8” pitch would be more top end speed and a bit less peak RPM?
 
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dwaynesda

dwayne
Apr 27, 2003
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dwayne
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Cabo 216
Each inch of prop on the pitch equates to about 200 rpm on average. You might have to try a couple of propellers.

Rpms will allow the motor to develope its horsepower, which is always rated at the high end of the rpm. The closer you get to the max rpm, the more horsepower you develop. You should be able to get up on plane no problem.
 
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marlyn

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  • Dec 18, 2005
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    21' skiff and 12' portabote recycled from milk jugs
    Dwaynes right the 4blades not helping,4 blades give you better mid range and power for pulling weight but sacrifice top end.I just left montana and im in idaho now but i was suprised at the size of some of the lakes up here,you could easily use a 25 on that size boat up there but i think you can get by with the 15 with a little tuning.
    I may be joining you soon!
     
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    slief

    Registered Lurker
    Jun 8, 2007
    507
    12
    Whitefish, Montana
    Name
    Scott
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    14’ Crestliner Sportsman
    Dwaynes right the 4blades not helping,4 blades give you better mid range and power for pulling weight but sacrifice top end.I just left montana and im in idaho now but i was suprised at the size of some of the lakes up here,you could easily use a 25 on that size boat up there but i think you can get by with the 15 with a little tuning.
    I may be joining you soon!
    Where in Montana were you and where in Idaho are you now? Yeah, we have some decent sized lakes out here. The biggest nearby being Flathead lake and then Koocanusa which is also near by. We have a lake less then 1000’ from our doorstep which I fish all the time and several others within a few miles in any direction. I’ve been using the hell out of my boat since the ice melted. The boat is rated for up to 35HP and would benefit hugely from a bigger motor but at that point, I‘d be better served selling this boat and getting a different boat with a bigger motor as the motor costs alone are cost prohibitive. Granted I could easily sell my Honda 15. Unfortunately, spending that kind of money right now isn’t on the agenda. Heck, if I could get this thing going 15mph, I’d be thrilled but altitude is working against me! I just ordered a 3 blade 9.25 x 8” and a 3 blade 9.25 x 7”. I figure if the 8” does the job at my current elevation, the 7” would help at higher elevations. Hopefully it works out that way but I will test both props on the lake next door to see how they perform. Just hoping either of these props makes a big difference in the top end. The other thing I am wondering about is a hydrofoil but since I have a manual tilt setup, I don’t know how worthwhile the addition would be. They made a huge difference on my Glacier Bay but that had twins and much bigger motors.
     
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    marlyn

    I Post A Lot But I Can't Edit This
  • Dec 18, 2005
    8,707
    5,205
    So Cal
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    mark
    Boat
    21' skiff and 12' portabote recycled from milk jugs
    Where in Montana were you and where in Idaho are you now? Yeah, we have some decent sized lakes out here. The biggest nearby being Flathead lake and then Koocanusa which is also near by. We have a lake less then 1000’ from our doorstep which I fish all the time and several others within a few miles in any direction. I’ve been using the hell out of my boat since the ice melted. The boat is rated for up to 35HP and would benefit hugely from a bigger motor but at that point, I‘d be better served selling this boat and getting a different boat with a bigger motor as the motor costs alone are cost prohibitive. Granted I could easily sell my Honda 15. Unfortunately, spending that kind of money right now isn’t on the agenda. Heck, if I could get this thing going 15mph, I’d be thrilled but altitude is working against me! I just ordered a 3 blade 9.25 x 8” and a 3 blade 9.25 x 7”. I figure if the 8” does the job at my current elevation, the 7” would help at higher elevations. Hopefully it works out that way but I will test both props on the lake next door to see how they perform. Just hoping either of these props makes a big difference in the top end. The other thing I am wondering about is a hydrofoil but since I have a manual tilt setup, I don’t know how worthwhile the addition would be. They made a huge difference on my Glacier Bay but that had twins and much bigger motors.
    We were in Flathead valley area,polson,bigfork,kalispell,nosed around missoula then to gardiner and a day driving through yellowstone and grand teton and into victor and driggs idaho,were bouncing around twin falls/buhl/snake river area now but have to return soon.The first 4 days we were in snow but it was perfect the day we hit flathead valley then snow again through yellowstone.Were already planning another trip to check more areas we didnt have time for in 2 weeks.Next time we will probably fly up and rent a car to save some time.While were not huge fans of the winter weather we are of the area,californias great and i love it but im done with the politics and population.
     
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    slief

    Registered Lurker
    Jun 8, 2007
    507
    12
    Whitefish, Montana
    Name
    Scott
    Boat
    14’ Crestliner Sportsman
    We were in Flathead valley area,polson,bigfork,kalispell,nosed around missoula then to gardiner and a day driving through yellowstone and grand teton and into victor and driggs idaho,were bouncing around twin falls/buhl/snake river area now but have to return soon.The first 4 days we were in snow but it was perfect the day we hit flathead valley then snow again through yellowstone.Were already planning another trip to check more areas we didnt have time for in 2 weeks.Next time we will probably fly up and rent a car to save some time.While were not huge fans of the winter weather we are of the area,californias great and i love it but im done with the politics and population.
    We are just outside of Kalispell. I love love love this area! So many lakes and rivers to fish. I actually love the winter as that brings on ice fishing and easy access to different spots on lakes that you can’t get a boat into. I picked up a snowmobile as soon as we moved here so I can get out onto the different lakes around me. I have a little trailer sled, my ice tent, heater, small portable grill etc. I hit 12 to 14 different lakes this last winter and caught a ton of fish. The nice thing for me is that I can hop on my snowmobile and take off out of my driveway and ride to several different lakes around here to fish. I also have good winter gear so I’m never cold and the heated ice tent on those really cold days makes all the difference in the world when ice fishing.
     
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    surf launch

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    Dec 27, 2006
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    San Diego
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    Rob
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    14 ft Livingston and 12'aluminum skiffs
    Knew a guy who ran the boat consession at Lake Crowley (around 7000') and the first thing they would do when taken delivery of new outboards is change out the factory stock prop to one of a much smaller pitch. This usually compensated for the altitude problem without carb/jet modifications.
     
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