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I have a 1970 Sport with the original 1969 25 HP engine on it.

So far top end is 22 MPH on GPS.

Is this the reasonable top end with the old motor or are there options to increase that with a propellar swap. I Honstely don't know what prop is on it now. I have seen options for the older motor but don't want to spend money as shots in the dark.

Thanks

Chris

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That boat, with a motor putting out 25 HP, should be running in the low 30's. Without more info, it's hard to know where exactly your problem is. Could be many things; water in the hull, incorrect prop, motor running poorly, etc.

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I read yor post here and the one about the tiller model ,you said you only get about 7MPH out of a 15HP. Your hull must be pretty heavy ,that 15HP should plane a 13 no problem. As far as the 25 is concerned I had an old 33 johnson on my 13 when I was a kid and that thing was fast ,well over 30MPH . I would check the wieght on it and see if water is getting in some where

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Chris,
To determin if a prop swap will help you need to know what prop you have and the RPM's and speed at WOT.

Possibilities for poor performance include, engine trouble, hull weight, incorrect prop among them.

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Thanks.

The boat sat outside untarped for quite awhile before I got it. I am afraid it may be waterlogged.

Is the drill a hole in the bottom and let it drain a realistic way to get it to drain out? The bow has been rasied for quite awhile over the winter here, so I am thinking that much of the water may have run to the back already and may be ready to drip out.

Any suggestions for hole size or number of holes?

Chris

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You will never get all the water out by draining, at least not in time to use the boat any time soon.
Alaskan Squall

If you don't know the weight of the boat you should find a scale and figure that out first. It is the only way to know the hull holds water before you start drilling a lot of holes.

Does the boat have a Tach and a GPS? Do you know what prop is currently on the boat, or can you at least pull off some numbers?

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I looked at the prop and didn't see any numbers on the outside although maybe if I pulled it I could find something somewhere else. I measured the diameter at 9", but don't know the pitch.

I ran it on the GPS and was getting 22 MPH WOT.

Now that I think about when the previous owner had it, and when it was always kept covered (20 years ago), he said he ran it against another boat then and he said he was always right around 22-24 +/-.

What would an ideal prop size be for the motor? I have seen 9X10, 9X10 1/2 and 9 1/4X11. This is for a motor size from say 15-25 HP. If you jump to say a 25-33 HP range then the prop sizes go up to 10 1/2 X12, 10 3/8X12. I think these would be way to big for an old motor.

What requires more torque to turn, a bigger diameter or a higher pitch?

I am thinking the 9 1/4"X11" may be a good choice. I would be willing to gamble once but not reapeatedly.

I need to find an easy way to weigh this boat. I have a 450# scale and may be with a good pulley system (Chain hoist), I could lift it.

Thanks for the help, I'm not a speed demon, but I'd at least like to be able to get the most out of it.

Chris

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Chris,

First of all I would pull the prop and see what it size it says.

Second, we know it is a 1969 Johnson 25 hp...

Third, do you have a tachometer? This is really necessary to see if a prop will help.

Fourth, prop diameter and pitch.
We have NO choice on the diameter. That is left up to the propellor engineers who design the props.
The consumer buys a prop by the pitch and brand. Again, forget about the diameter... Only the pitch and brand.

If you have a tach and aren't running near the RPM's for that engine at WOT, then you need to drop down in pitch. If you are running too many Wide Open Throttle RPM's, then you move up in pitch or try a different brand that has the same pitch but might be more aggressive.

You really need a tach to fine tune any boat/motor combination with the correct prop.

However, let us know the exact size that is stamped on your prop now.
These guys should be able to able you get going in the right direction.

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For what it is worth, this is how I weigh small boats with bathroom scales:

You will need 2 or 3 strong buddies. 3 will be better. Have your buddies come over to help you and tell them bring their bathroom scales.

Place one person and one scale at each corner of the boat (assuming 3 buddies + you = 4). The four of you pick up the boat, step on your respective scales, and note the weight on each scale. Now set the boat down, everybody step back on the same scale, and read the weights again. Do the math and you have the total boat weight. It doesn't matter if one person carried more than another because we only care about total weight.

Your buddies can't be too burly or fat or the scales will bottom out. Each scale must be on a flat smooth surface or it won't work.

Good luck.