[tangler]

When it comes to small boats, there is clearly a minimum level of power required to get a boat on plane at altitude. I believe that 75HP is likely enough power to get a 15-17 ft. boat on plane up high.

Does anyone on here have a 15-17 ft. boat with a 40-60HP outboard? What kind of performance are you getting at altitude (up in the mountains, not front range).

MPH/RPM/outboard type/prop pitch?

 

[IFSHDOU2?]

I had a 16' Lund Pro Fisherman Tiller (1984) That I had equipped with a 40HP Johnson.... Worked like a champ... Lost a bit of HP at altitude (11 Mile; Grandby; Taylor etc) but no big deal...

 

[slayerfish]

My last boat was a 1992 17' Tracker, side console, 60 hp 2-stroke. I ran a 14 x13P prop. Had a 14x15P that I could only run down at 2000' elevation.

Anyway, with the 14x13 I got 34MPH at the Crack, 29MPH at 11-mile. GPS speed from the Lowrance.
Got like 23 mph at Taylor res.

14x15 at Fort Peck I got like 37-38 MPH.

Never checked rpm much wide open is wide open. Seems like wide open was 6000.

 

[hobiecat]

Prob pitch and size has been mentioned. You definitely want the right prop. Can you max out the rpms. I think there are a couple of places that will let you demo props with a deposit.

How much does the boat weigh? How much does your passengers and their gear weigh? What's the weight distribution in the boat? Smaller boats are pretty weight sensitive. Is it just you and Boon in the boat? Or, you Ovey and Riv? Makes a difference.

How can you help the boat? The right prop is a given. Smart Tabs or even manually adjusted trim tabs can make a big difference. Hydrofoils give a cheap boost in performance...especially when it comes to planing out or the ability to run flat at slower speeds without the bow pointing to the sky.. And we could talk about jetting...but if using the boat at both high and low elevations..that could be a pain.

 

[hobiecat]

Forgot to mention. I had a 13 foot Glastron with a 90 horse that would run 52 at Pueblo. But would only run in the low 30's at the mile. Had a 14 foot Glaspar with a 40 horse that would only run 28 at Pueblo and maybe 17 to 18 at the mile. However, I used the same props on both Pueblo and the mile.

 

[tangler]

Hobie, I could talk for hours about all of this. Your questions are all valid and I have dissected all factors ad nauseum. Slayer and IFSH's responses are what I expected to hear and confirm some suspicions I have. The suspicion being that there is under-performance with my outboard rather than it not being strong enough outright.

I'm pushing a 16 ft. aluminum Fisher with a 50HP Mercury EFI 4 stroke. Without typing a book, some key tests are that I cannot get this boat fully on plane at Eleven Mile when I am alone with a 9P 3 blade prop. I neglected to mark down the RPMs but I'm guessing that they were around 5.5K and barely touching 20MPH. I also ran the boat alone at Blue Mesa alone with a 7P 3 blade prop and could not rev limit the RPMs.

Obviously, when I start adding people things go downhill from there.

The boat has a hydrofoil, but that seems to just change the angle of the hull to allow for the least water resistance... while not on plane. Boon and I took the hydrofoil off at Willies with the 7P prop and it was a disaster... no hull angle control.

My brother and I got the boat up to 23 MPH on Chatty last year with no gear, and he is my size. The outboard starts instantly and idles well. I have changed plugs, fuel filter, and have a new primer bulb coming in the mail. I see people at these lakes with more people in their boats and smaller motors on plane...

 

[slayerfish]

7 pitch prop? Somethings wrong big time. Are you cruising around with the anchor out?

 

[hobiecat]

Do you have power tilt and trim? Which trim hole on the motor mount are you using? Is the motor mounted high enough on the transom?

 

[tangler]

Power trim, yes. Motor is mounted in the lowest holes on transom but the anti cav plate is right where it should be in relation to the keel (even). Boon thinks is't a smidge low but I have a hard time believing that that would cause this much of a problem. We're talking like a quarter inch low.

 

[slayerfish]

7 pitch is terribly under-propped. 1/4 inch will make no difference. A 4 stroke normally uses a higher pitch than a 2 stroke anyway. Have you tried a taller prop?

 

[hobiecat]

Just asking, but I'm sure you've tried moving more weight to the bow.

 

[slayerfish]

Just asking, but I'm sure you've tried moving more weight to the bow.

Hobie, a 50hp 4 stroke with a 7p prop? Thats unheard of- Moving weight around aint gonna help anything-

 

[tangler]

I have. However, those hydrofoils will hold the bow at an angle basically regardless of where the weight is depending on the trim. When we removed the foil there was absolutely no hope, it went even slower and trimming had zero affect.

 

[hobiecat]

When you say it won't plane out...you're talking riding bow high ...rather than the boat plowing...Is that correct?

 

[tangler]

Slayer, if I use the 9P in the mountains I just get lower top end. There isn't enough power to turn it. So, if I have 2 small passengers the 9P might get me up to 12 mph where the 7 will go 15mph. It's AIDS.

 

[tangler]

When you say it won't plane out...you're talking riding bow high ...rather than the boat plowing...Is that correct?

It won't plane out = no matter the trim level that thing is plowing water. It's kinda gotten on plane at PLO around 22mph but the foil is still buried in the water. Can't even see it.

 

[slayerfish]

Slayer, if I use the 9P in the mountains I just get lower top end. There isn't enough power to turn it. So, if I have 2 small passengers the 9P might get me up to 12 mph where the 7 will go 15mph. It's AIDS.

Bummer.

 

[tangler]

I got some answers here in that people with smaller and similar motors are able to get more output at altitude, which is what I thought was the case. If this thing was performing properly, I shouldn't have these issues. I believe that I need to take it in to have a pro look at it at this point. I have gone through all the basic troubleshooting that I am capable of.

 

[hobiecat]

So, if I'm correct. Setting aside your power tilt for a moment ...you said your thrust rod is mounted in the hole nearest the transom? Is that correct?

As far as hydrofoils go, I've had them on five boats and always used them to get the bow down to get on plane.

 

[hobiecat]

I was assuming that you couldn't get your bow down. Plowing..motor needs to move out and up and/or weight needs to be moved to the stern.