27 MPH is ALL?

[HotKetchup]

Didnt know which forum to post this in so I figured Id start here. Heres my boat...1960 14' Olympian runabout style converted to a bass boat. pretty lightweight little boat. I have a West Bend made 1960 Firestone 40 HP motor. ALl I can squeeze out of her is 27 mph. I sure wouldve thought a 40 hp would have a bit more speed than that. Motor seems to be running great. Starts with the touch of the key. Idles and accelerates smoothly. New plugs and tore down and rebuilt carb with not much difference. Ive tried all different motor tilt settings. the best is actually all the way out. getting that sharp front "V" out of the water. Im guessing hull design may be the culprit? Theres no pitch ratings stamped on the prop just "A94265". Any info on this # would be awesome. From the research Ive done, this year 40 hp usually came with a 10.5 x 12 prop. Thats on Evinrudes. This motor...I got nothin.

Oh yeah threw some home made trim tabs on to get the stern out of the water a bit. It did that just fine with very little effect on speed.

ANy suggestions / inputs? Thanks!

 

[kenmyfam]

Re: 27 MPH is ALL?

Motor looks a little low from the photos but that could just be the angle it was taken. How is the cav plate in relation to the bottom point of the transom ??

 

[HotKetchup]

Re: 27 MPH is ALL?

ABout 1" below the bottom of the transom.

How about fuel delivery?? Each cylinder has its own fuel pump. typical diaphragm style. Would old, stretched out diaphragms keep it from reaching full potential?

Its weird, everything Ive "thought" would be a problem has all been good.

ALso the 27 MPH was taken with a GPS.

 

[5150abf]

Re: 27 MPH is ALL?

Back in 1960 HP was measured at the prop so in modern terms it would be a 30-35 horse so I think you are about right.

I have a 16' aluminum fishing boat with a 50 and it does 28-30 GPS.

You cna try moving the engine up another notch but like I said I think you are getting about all it has.

If the engine runs the fuel pumps are fine, don't think that would make much if any difference.

 

[a70eliminator]

Re: 27 MPH is ALL?

I think you said that backwards, HP measured at the prop is going to be less than if measured directly from powerhead due to parisitic loss through the gears and rotating mass. I think.
How many RPM is your motor turning? You probably already know the highest pitch you it can handle while remaining in RPM operating range for speed.

 

[Chinewalker]

Re: 27 MPH is ALL?

14-footer with electric motor on bow, likely an extra battery, other bass accessories, running a 50 year old motor of approximately 35 horsepower (if all is perfect). I'd say you're doing alright.

The above hints and advice are spot on for maximizing what you have.

- Scott

 

[Andy in NY]

Re: 27 MPH is ALL?

you also have to consider that boats max speeds are limited by hull length. you could put 1,000 hp on that boat, but its never going to go as fast as a 30' boat with the same hp.



but like everyone else said, you are in the normal range for a 14' with that hp. i had a 14' tri hull with a 50 hp merc on it and some extra weight in the hull die to water logged deck and stringers and foam, and ran about 28. my 16' tinny with a 50 rude on it runs 26 with 5 people.

 

[HotKetchup]

Re: 27 MPH is ALL?

I think you said that backwards, HP measured at the prop is going to be less than if measured directly from powerhead due to parisitic loss through the gears and rotating mass. I think.
How many RPM is your motor turning? You probably already know the highest pitch you it can handle while remaining in RPM operating range for speed.

I was under the understanding that if 40 HP at the prop, youre getting 40 hp performance. If measured at the head like today, then by the time it reaches the prop, the prop hp will be a bit less.

Not that it makes a difference in my case. I really just wanted some confirmation that Im getting all I can get out of my motor. I suppose Im getting all I can from her now. I figured as much but just wanted to be sure by comparing notes with other boaters with similar rigs. My brother in Louisiana claims he's pushing a 16' aluminum - medium weight bass fishing rig - 37-40mph with a 91 johnson 25hp. I think he fell off the boat and hit his head on a stump. (Ill send him a link to this thread - hi Gary)

I guess all thats left to fully convince me is hook a tach to it and see my full throttle RPM's and if a higher pitch prop may do me some good.

 

[HANGEYE]

Re: 27 MPH is ALL?

I was under the understanding that if 40 HP at the prop, youre getting 40 hp performance. If measured at the head like today, then by the time it reaches the prop, the prop hp will be a bit less.

Not that it makes a difference in my case. I really just wanted some confirmation that Im getting all I can get out of my motor. I suppose Im getting all I can from her now. I figured as much but just wanted to be sure by comparing notes with other boaters with similar rigs. My brother in Louisiana claims he's pushing a 16' aluminum - medium weight bass fishing rig - 37-40mph with a 91 johnson 25hp. I think he fell off the boat and hit his head on a stump. (Ill send him a link to this thread - hi Gary)

I guess all thats left to fully convince me is hook a tach to it and see my full throttle RPM's and if a higher pitch prop may do me some good.

I have a 97 Smoker Craft 1440 Pro Mag with a 98 Mariner 25hp and have tried moving weight (anchors-batteries) fore and aft and have even left the anchors on shore. Best I can get out of it is 27.2 on the GPS. Hmmm, 16' tinney with a 25 and he's getting 37-40mph? I think he needs to calibrate his GPS, try a different one or.........WATCH OUT FOR THEM STUMPS. Just doesn't seem plausable IMO. But i digress, I have been proven wrong before. LOL

 

[tschmidty]

Re: 27 MPH is ALL?

you also have to consider that boats max speeds are limited by hull length. you could put 1,000 hp on that boat, but its never going to go as fast as a 30' boat with the same hp.

That's only true for displacement boats, has no consideration on planing boats.

 

[TerryMSU]

Re: 27 MPH is ALL?

I used to have a 14 ft fiberglass tri-hull with a 35HP Johnson (mid 1970s vintage). Top end was about 28MPH with just me in it and a front trolling motor. This hull had rather badly water saturated foam. As far as your brother, no way is that combination going that fast. I have a 15.5 ft aluminum hull bass boat with a 1990 40HP Evenrude. Top end is 30mph.

TerryMSU

 

[Lion hunter]

Re: 27 MPH is ALL?

Hotketchup,
On older motors (probably up to early 80's) HP was measured at the head and the actual HP at the prop was probably 10%-15% less, so your 40 is more like a 35. From the 80's on the HP is measured at the prop, so a 40 is a 40. Assumimg they are setup and running correctly.