Thought my boat would be faster

[Mike Lukacevic]

I’ve got an 81 MFG Piper 1500 with 120 Mercruiser in it. It weighs 1350 lbs. it’s got a 15x17 p prop on it. Admittedly, the prop has got some significant wear to it.
Considering the size and weight of the boat, with two adult guys(500) in it, I thought if get better than 30.5 mph. Bummer. The engine runs fine. Great compression, 140 across the board. Guess I should checked the rpm, but didn’t seem like it was digging at all. Any thoughts? It was trimmed all the way down cuz the hoses leaked out. Now fixed. Does this seem about right?
I’ve only had 16 ft StarCraft SS with a 75 and that thing will do 43 easy trimmed up.

 

[Scott Danforth]

Can't compare an aluminum outboard boat to a fiberglass I/O

What RPM are you turning?

You sure about your weight? May want to find a scale

 

[airshot]

Yep...gonna find your boat is probably heavier, and probably water logged, also trimming out will gain speed, gotta have the proper RPM, cant tell by ear!!

 

[Mike Lukacevic]

Yep...gonna find your boat is probably heavier, and probably water logged, also trimming out will gain speed, gotta have the proper RPM, cant tell by ear!!

I’d be REALLY surprised if this thing is waterlogged. The floor and transom are solid as a rock. It’s been babied. I’ll get back when I take out to get the rpm.

 

[Mike Lukacevic]

1981 MFG PIPER1500. small boat with this 120 Mercruiser.

 

[jimmbo]

only 120hp, 30mph doesn't seem too far off. Put one of the Guys in the Back Seat see if that improves the Boats Trim, and speed

 

[matt167]

Yup. 30mph would be about right.. but if you didn’t have a speedometer, would you know? would you care?

 

[airshot]

I’d be REALLY surprised if this thing is waterlogged. The floor and transom are solid as a rock. It’s been babied. I’ll get back when I take out to get the rpm.

Not to burst your bubble but...I would be really surprised if it wasn't water logged ! Feeling solid as a rock means nothing in glass boats, there are hundreds in junk yards the feel solid. Again, I mean no disrespect....but a 1981 glasser with wood structure issues would have to be stored inside its entire life. You have a far better chance of winning powerball than having a non structure issue with a boat that old. Testing is fairly simple, how much are yo willing to bet your life on. Does it take in any water when you have it on the lake? How much water comes out when you pull the plug after an outing ? Cool looking boat, I hope she is good on the deep inside

 

[Mike Lukacevic]

Not to burst your bubble but...I would be really surprised if it wasn't water logged ! Feeling solid as a rock means nothing in glass boats, there are hundreds in junk yards the feel solid. Again, I mean no disrespect....but a 1981 glasser with wood structure issues would have to be stored inside its entire life. You have a far better chance of winning powerball than having a non structure issue with a boat that old. Testing is fairly simple, how much are yo willing to bet your life on. Does it take in any water when you have it on the lake? How much water comes out when you pull the plug after an outing ? Cool looking boat, I hope she is good on the deep inside

I like this reply. I’m sure it was redone. At least the floor and all the interior has been. It’s not taking on water. But. I’m 63. It’ll outlive me and I’ve had fun screwing around with it. It is pretty cool, ain’t it?

 

[Mike Lukacevic]

Yup. 30mph would be about right.. but if you didn’t have a speedometer, would you know? would you care?

That’s what my buddy said. Wow. Is this fast!

 

[Mike Lukacevic]

only 120hp, 30mph doesn't seem too far off. Put one of the Guys in the Back Seat see if that improves the Boats Trim, and speed

I will. If I can find a friend that’s not a fat ass and shoehorn him into the jump seat.

 

[airshot]

I like this reply. I’m sure it was redone. At least the floor and all the interior has been. It’s not taking on water. But. I’m 63. It’ll outlive me and I’ve had fun screwing around with it. It is pretty cool, ain’t it?

If its already been upgraded then your good to go !! Get your max rpm at wot and see if that matches the max rpm rating on the motor....that will show if you have the right prop on it. Gotta post some pics or her in action !!

 

[Scott Danforth]

iff and that is a big if..... the 2.5 runs perfect, the prop is perfect, the winds are perfect and the boat actually weights 1350#, then the boat could do upper 30s and may hit 40 mph. that is based on my old 16 foot boat (that did weigh the 1650# it was supposed to after I did the transom) with a 3.0 that would do 40-41mph with two people

I suspect the motor is not spinning to top RPM and the boat is a bit heavy

 

[nola mike]

Growing up had an '82 Galaxy 16' with a 120 OMC, it would hit mid-upper 30's

 

[QBhoy]

Late 30’s would be good going gps I’d say. Trim and good prop is required. My boat will loose 10 mph or more without trim

 

[Grub54891]

I have an old 17.5 chapparal. !983, mercruiser 120. She's beat and at the end of life. It will do about 35 mph by myself, with two onboard, it's about 30. If I put the proper prop on it may do better but it's going away next spring. I bent the prop that was on it before I had a chance to test it but the spare was there and I stuffed it on. My 85 Larson will be done being restored by spring.

 

[Mike Lukacevic]

I have an old 17.5 chapparal. !983, mercruiser 120. She's beat and at the end of life. It will do about 35 mph by myself, with two onboard, it's about 30. If I put the proper prop on it may do better but it's going away next spring. I bent the prop that was on it before I had a chance to test it but the spare was there and I stuffed it on. My 85 Larson will be done being restored by spring.

Thanks for the reply. Your Larson has 2 more foot on mine