power head hp vrs foot hp.

[derwood]

hey guys,<br /> i am looking for a motor for the center con. that i am building. my freind has done this to his boat and they are identical boats. Owachita 17fters. ( buy the way when the guts are out and the decks are redone and fitted with center cons. they are small but awesome boats.) anyway he has a brand new 25 hp and it puts his boat on plane almost like posiden himself lifted it strait up. no lie. it planes level in less than his boat lenghth. jumps right up there and that is why i searched far and wide for this boat. now i can't afford a new 25hp motor and he said that his 25 has 40 at the prop and 25 at the power head and if i want to get and old motor that i will have to get a 40 hp to get the same results. dose this sound right. im sure that i can find a 40hp for the 400.0 bucks that i have. it won't be new but in Fla. they are'nt that hard to come by. thanks derwood.

 

[JB]

Re: power head hp vrs foot hp.

Howdy Derwood.<br /><br />Your friend is confused. Gearcases use horsepower, not generate it.<br /><br />If his engine is a 25, almost any 25 hp rated at the prop will do the same for your boat.<br /><br />Good luck.<br /><br />JB

 

[skier]

Re: power head hp vrs foot hp.

In 1981 or 1982 the marine industry went from powerhead rating to prop rating. To get the same prop hp on an older motor take the hp rating adn subtract about 10% and you'll get as close as you can get. To give an example, I have a 1979 Merc 140hp at the powerhead, at the prop it is pretty close to a new 115hp. I calculated it and I have about 126hp at the prop so it's not exact. Or an old 30hp will give you 27hp at the prop. <br /><br />I hope this helps.<br /><br />Craig

 

[novacane]

Re: power head hp vrs foot hp.

same thing with the auto industry starting in 1973<br />thay took hp ratings at rear wheels inlue of the flywheel rating which is appox 10% more than at the the rear wheels hmmm sure would like to invent a lower unit that would make extra ponies <br />i be a rich man

 

[derwood]

Re: power head hp vrs foot hp.

Hello guys'<br /> Yea, thats what i thought. it seemed to be kind of funny to me when he said that , but i don't know all that much about boat motors yet. i can fix the small ones but i don't have any experiance with the big ones and so i asked the gentalman that know whats up. I still think that i will get a slighty bigger motor than his 25 but not much bigger because i don't want to add very much weight to this already well matched setup. i hope to get a 30 or 40 hp motor with out gaining to much weight. i would like a hair bit more top end speed than him because of the peekaboo T storms that happen in Fla. They can and do pop up out of nowhere. thanks for the help guys. i will post a few more questions before i am done with this boat. knowlage is power( if i could only spell )

 

[G DANE]

Re: power head hp vrs foot hp.

Hi derwood<br /><br />I would recommend you to look for a mid/late 1980ties evinrude or johnson 35 HP. There is a 80 lbs weight increase from 35 to 40 HP, both propmesured since 1984 models. Great motors both, i owned 3 now ! 35 is a crossflow untill 1992 i think, 40 HPs are loopcharged from around 1975.<br /><br />If your 17´isnt too heavy, you will do great with 35Hp - i have 35HP on my swedish 16´Ørnvik it does 26 KPH ! or almost 30 miles when im alone.

 

[derwood]

Re: power head hp vrs foot hp.

G Dane,<br /> thanks for the tip on the weight. i would rather go with the lighter motor. do they come in a short shaft? the 17 fter is actualy a 16 fter ( i measured it yesterday) i picked it up at the county dump for 8 dollars. the foam on the inside was waterloged and the plywood under the fiberglass deck was jelly. all the stringers seem to be in good shape as they were all coverd in fiberglass. when my freind did his he found that all his stringers where made of mohogany. i have taken the foam out and i need to replace the transom with that new pour in transom stuff. once i do that i can redo the deck and foam. the rest of the boat was mint. i bet i took out 600lbs of wet foam. it took a forklift to get it on my trailer but now i can move it arround buy myself as the boat itself is not a heavy one. a 35 hp would be just right in my book. the front of this boat is trihull and the back 2/3rds is close to flat with a slight v. my freinds boat rides very smooth and with the 25 hp (new) is not so fast as to be scary but is suitably quick. i just like that xtra boost for those t storms. it won't be very much faster i would'nt think. thanks Derwood