HP at shaft or propeller

[strokersquid]

Just bought a boat ( 17 ft Arima Sea Ranger ) with a 1993 100 HP Mercury 2st on it . Looks like this weighs about 300 lb. If I want to repower, all the avaliable engines at 115 HP weigh quite a bit more. If one goes to a 90 HP I can get an Optimax that weighs about the same. On a different forum they said not to worry since at that time HP was not measured at the propeller and a newer 90 HP would actually put out MORE HP since it IS measured at the prop now. Is this true ?

 

[tx1961whaler]

Re: HP at shaft or propeller

In 1993 all were rated at the prop.

 

[strokersquid]

Re: HP at shaft or propeller

In 1993 all were rated at the prop.

I was afraid of that. Would the 50lb or so difference be huge ?

 

[tx1961whaler]

Re: HP at shaft or propeller

Probably not. That boat is rated for a 120 hp max., has an 8 foot beam, and commonly has a kicker motor. The "suggested engine" hp from the mfg is 75 hp, so you may not lose much if you went down to a 90.

 

[strokersquid]

Re: HP at shaft or propeller

thanks.i'm surprised there's little choice between 90 and 115 HP.

 

[bassman284]

Re: HP at shaft or propeller

I doubt 50 lb or even 100 will be noticeable, for the most part.

I have a Lund 1650 Explorer (lighter than your boat) with a 75 hp max. I have a 60 4 stroke (248 lb) and added a 105 lb 9.9 4 stroke kicker. The only noticeable difference to me was my tongue weight got light enough to cause a little sway so I had to move the axle a bit. Don't really notice it on the water.

You don't say what motors you're looking at, but I'll use new Mercs for reference:

In the Optimax, the 75, 90, 115 and 125 all weigh 375.

In 4 stroke, 75, 90 and 115 all weigh 399.

It seems generally that newer motors of any given hp run heavier than older motors of the same hp.

 

[Chris1956]

Re: HP at shaft or propeller

Merc 115HP motors of the 90' and newer vintages are inline 4 motors. I would think they weigh nearly the same as your 100HP motor.

I am not sure the performance will be a lot different with a 15% increase in HP.