16ft FB Boat, 50 HP, only goes 10mph

[dan1979]

Hello fellow boaters! Just came across this forum and was hoping someone might be able to help shed some light on my problem. I just finished my boat after 2 slow years of working on it and noticed a major problem when at the lake.

I have a 16ft boat, V-Hull with a 50HP Force motor and I am only able to get about 10mph out of it. I called the local boat shop and they told me to check the position of the motor in reference to the bottom of the hull. At first, it was about 4 inches to low, so I raised it up to be in line with the bottom of the hull. I hoped that would fix it, but I ran it again and the same problem was there. Actually, almost worst.

The engine seems to be running good, sounds like I am getting full RPM's out of it, but just not at the prop. I checked to see if I had a spun hub in the prob, but it looked good. I took the prop off and tried the turn the hub (with channel locks) while holding the prob and it was very tight so I don't think I have a spun hub.

I have been told by several people (and marine stores) that I should be getting anywhere from 24-30mph from this motor. Which is really all I want. 10mph seems way to low.

Has anyone ran into this problem before? Any help would be greatly appreciated.

Thanks!!

Dan

 

[tashasdaddy]

Re: 16ft FB Boat, 50 HP, only goes 10mph

did you remove the prop and mark it as the picture below? if not you have not properly tested the prop. have you checked compression and spark on both cylinders, the motor sat up for 2 years, did you awakening it properly?
http://forums.iboats.com/showthread.php?t=158086 did you clean the carbs? moving to force forum.

 

[dan1979]

Re: 16ft FB Boat, 50 HP, only goes 10mph

Tashasdaddy, hey thanks for the quick reply. I haven't marked the prop yet. The prop I have on my outboard is a smaller version of what you shown. It has the black cone on the outside with a cotter pin in it. I took the pin out, unscrewed the black cone, then tried turning the hub with a pair of channel locks while someone else held the prop. It didn't budge.

It the hub is spun wouldn't I be able to turn it a bit? I haven't checked the compression yet, and there is spark going to both cylinders. The motor sat in my garage for about 1.5 years.

Thanks!

Dan

 

[jerryjerry05]

Re: 16ft FB Boat, 50 HP, only goes 10mph

You don't have enough strength in your arms to turn a spun hub.If you could spin it by hand your boat wouldn't move at all.Only if you put some kind of lever on it would it turn.That motor puts out way more power than you can imagine. Do the comp test and then get another prop.Jerry

 

[dan1979]

Re: 16ft FB Boat, 50 HP, only goes 10mph

Jerry,

Hey thanks for the reply. I will put a mark on the hub and prop and take it out to see if I have a spun hub. I skimmed through a few other posts and think it might be a good idea to go ahead and replace some gaskets, clean the carbs, replace lower unit oil, and etc... since the motor hasn't ran this much for a couple years.

I am pretty new to boating, so if I do have a spun hub, do I need to buy an entirely new prop? Or just a hub? My prop seems a bit on the small side, but looks like it might be the only option for this motor. I attached a picture. Could I replace with a larger prop, or is that a bad idea?

Thanks!

Dan

 

[jerryjerry05]

Re: 16ft FB Boat, 50 HP, only goes 10mph

Keep the same prop. Bigger would probably only lead to performance problems .Buy newI don't think anyone rehubs anything that small.Jerry

 

[dan1979]

Re: 16ft FB Boat, 50 HP, only goes 10mph

I looked on iboats and found some props.. Kind of pricey.. If I bring the prop to a Marine Shop would they be able to check if its "spun" I'd hate to buy a new prop if I don't need to.

Here's one I found:
http://boatpropellers.iboats.com/Fo...1/322/?**********=570018114&*******=144639943

Thanks,

Dan

 

[randys]

Re: 16ft FB Boat, 50 HP, only goes 10mph

...
I have a 16ft boat, V-Hull with a 50HP Force motor and I am only able to get about 10mph out of it. ...It has the black cone on the outside with a cotter pin in it. I took the pin out, unscrewed the black cone...

What is the pitch of your prop?

Not trying to be an iBoat.com newbie know-it-all, but I do have a '94 Force 40 and 16' boat. Same splined prop and drive pin attachment method. (Unless you have a 1995 or later Force 50, which would be a through-hub exhaust system that Mercury uses.)

My 1994 QuickSilver Accessories catalog lists 6 props with different diameters and pitches, referenced against intended use and approximate speed. It lists a low pitch prop intended for house/workboat use, and approximate speed range of 1 to 15 mph.

The pitch is usually stamped on the prop on the outside between blades. A prop with (10 3/8") X (12 1/2") diameter/pitch would put you in the 22-32 mph range, WOT. A prop with 10.5" X 7" is intended for 1 to 15 mph.

What is the pitch of your prop?

 

[dan1979]

Re: 16ft FB Boat, 50 HP, only goes 10mph

Randy,

I'm not sure what the pitch is. I will take a look when I get home here in a bit. The motor is a 1986 Force, 50HP. The previous owner did have this motor on a smaller boat so the pitch could possibly be wrong for my boat.

When I was running the motor yesterday at the lake I noticed that my speed seemed to be stalling, but the motor would still maintain a high RPM. Also, if I give it full throttle right out the gate it really dogs to obtain the whopping top speed of 10 mph. But the motor sounds great.

How fast does your boat go with your 40hp? I'm hoping to get around 25mph.. That would make me happy. All in all, my motor is sounding good, and fires on the first turn, no smoke, no funny noises.. Seems my problems are somewhere below the engine. (i hope its the prop)

Thx,

Dan

 

[dan1979]

Re: 16ft FB Boat, 50 HP, only goes 10mph

The only thing that is stamped on the prop is "278 10" Not sure what that makes out to be. Is this somehow the pitch? I took the prop off again for a further look, I don't see any sort of rubber bushing inside. It looks like its all metal to me. If its all metal, is it still possible to have a spun hub?

Also, would a marine mechanic/boat shop be able to examine the prop to see if its spun? Versus taking it on the lake? I can't take out on the lake again just yet, waiting on some new gaskets for the lower unit to come in.

Thx,

Dan

 

[randys]

Re: 16ft FB Boat, 50 HP, only goes 10mph

The only thing that is stamped on the prop is "278 10" Not sure what that makes out to be. Is this somehow the pitch? I took the prop off again for a further look, I don't see any sort of rubber bushing inside. It looks like its all metal to me. If its all metal, is it still possible to have a spun hub? ...

Alone, the "278 10" does not seem to mean anything.

However, checking the '94 Acc catalog in the Force 50 props section, the prop with Part Number P278 has a pitch of 10". The prop is on the low end of pitch for speed, and is for heavier boats. The prop is "proper" for your boat, and will push a fast boat moderately at WOT. That would place the motor pre-1995.

[B]Diam	Pitch	100-lbs	Length	Speed	Part#[/B]
10.5	15	up to 7	< 14	30-38	P275
10.375	13.5	6-11	14-16	26-35	P273
10.375	12.5	7-13	14-17	22-32	P293
10.375	11.5	9-15	15-18	20-30	P287
10.375	10	11-19	16-19	18-28	P278
10.5	7	23+	house	1-15	P296

Does your prop pitch mean you can only go "10 miles per hour"? I don't know. What speed measurement tool did you use? What is the overall weight of the boat?

I went out and checked the NOS (new, old stock) prop I put on my boat Saturday. It has the part number stamped on the "cone" side of the hub face, and "12 1/2" between the blades. It does not have the exact same marking system as yours, but Part and Pitch are clearly marked. The old prop, poorly painted black over Chrysler-white, was too gummed up to read the hub without a file or wire brush.

I went over what you wrote, and I don't see mention of the thrust pin or seal. Is the thrust pin and seal in place under the cone and cotter pin?

That prop has rubber between the hub and blades. It is just very thin. If you happen to have an old, buggered and abused prop as I do, you may see rubber "oozing" out of the space between hub and blades. Even when spray painted black...

Regarding propeller pitch: Propeller selection FAQ

 

[dan1979]

Re: 16ft FB Boat, 50 HP, only goes 10mph

Randy,

Hey thanks for the details on everything. So I took my boat into the shop today and they tested my prop and everything is ok, no spun hub. They also said the prop is also the correct size and pitch as well.

One thing we did figure out is that I might have been running the motor in the wrong position. My motor is a manual tilt/trim.. (which sucks haha) I think I was running the motor to far away from the boat/transform. I am going to take it out again and make it snug, almost resting next to the boat and see if that helps.

Just in case: Since the prop is fine, is there any other mechanical problems that I can look into if this continues?

Thanks,

Dan

 

[fishrdan]

Re: 16ft FB Boat, 50 HP, only goes 10mph

What type of boat is it, fiberglass, aluminum,,, and what is the max HP rating of the hull?

A buddy of mine picked up an older 16' fiberglass boat with a bad 75HP outboard and put a 50HP on it, it was a slug and wouldn't plane. Good enough to put around small lakes, but not big lake worthy.

 

[dan1979]

Re: 16ft FB Boat, 50 HP, only goes 10mph

fishrdan,

The boat is 16ft Fiber Glass V-Hull. The max HP for the boat is 135HP. I am guess that might be what it came with. I picked this 50hp pretty cheap so I went with it. The local boat shops tell me I should be able to get at least 20mph from it. (i hope their right)

I just need it to get from one fishing hole to another at a decent speed, no water sports or anything like that. Is it possible my 50HP isn't enough? One other thing I found today is that the rating of 50HP is at the flywheel, probably only 38-40hp at the prop.. Then not to mention I am a mile high (denver) and I will lose some power there as well.

Well, I guess the next thing for me to do is take it out one more time and adjust the manual tilt/trim to see if I can find a better position for the motor. If that doesn't help, looks like I need a bigger motor?

Thx,

Dan