Proper HP for the boat ....................

[Trauma King]

I have posted some topics about a boat I aquired and my intentions to restore it and the motor that was on it.It is a 1972 Thunderbird Apache 187 with a 115 H.P 1976 Mercury Thunderbolt 1150 in line 6 cylinder. I hear this was a monster of a motor in it's day and wanted to know if there is a "significant" difference in the power and running between the 115 and the 135 HP which is the max rating for my boat. This way I can ponder what I may want to do reguarding which power plant to go with. I am rather nostalgic and am apt to leave the original 1976 115 H.P. for reasons stated above.

 

[QC]

Re: Proper HP for the boat ....................

The difference in power is 20 . . . And if they are both running at their rated power that 20 extra ponies would be noticeable . . . Maybe as much as 5 MPH if that 115 is barely getting it done.

 

[109jb]

Re: Proper HP for the boat ....................

If you ask me, the proper power for any boat is the maximum indicated on the plate. That being said, my current boat is 10 hp under and my previous boat was 15 under and I don't really see changing them. I'd say that if you have everything for the current motor and it runs, give it a try. You can always buy another later and then sell the one you have.

 

[JB]

Re: Proper HP for the boat ....................

I tend to power/repower boats at about 70% of rated power.

I have noticed two differences:

1. 100% of rated power is a bit faster out of the hole and a bit faster at WOT; 2-4mph.

2. 70% of rated power uses about 50% as much fuel because it is usually a lot less weight on the transom and planes with less wetted surface, therefore less drag.

These comparisons were two JohnnyRude 70s replacing JohnnyRude V4 100s.

 

[marine4003]

Re: Proper HP for the boat ....................

I have posted some topics about a boat I aquired and my intentions to restore it and the motor that was on it.It is a 1972 Thunderbird Apache 187 with a 115 H.P 1976 Mercury Thunderbolt 1150 in line 6 cylinder. I hear this was a monster of a motor in it's day and wanted to know if there is a "significant" difference in the power and running between the 115 and the 135 HP which is the max rating for my boat. This way I can ponder what I may want to do reguarding which power plant to go with. I am rather nostalgic and am apt to leave the original 1976 115 H.P. for reasons stated above.

You may gain some speed but it will result more in the weight difference between a 70's iron monster and today's lighter computer controlled motors..the HP gain is nominal.for the sake of nostalgia,keep the "tower of power" it'll look great back there.

 

[anzomcik]

Re: Proper HP for the boat ....................

i believe in 1979 mercury changed the spot where they measure hp from the crank to the prop shaft. When they did that the made the 115 a 90hp, 135 came a 115... So you can think of your 115 as a 90hp by newer standards. i have an 1986 merc tower 90hp, i like it alot.

I have also checked out getting a newr merc and found that the four stroke weights like 85lbs more, optimax weights 75 more, and the base level weights about the same. the motors displacemtn was greater also like 1.5 liter verses 1 liter. I know new motors will run smoother, more effieient, but i am not sure it would be worth it looking at the whole picture.

 

[mthieme]

Re: Proper HP for the boat ....................

I think you should go with the 135.
Let me know where I can pick up the 115!