More Performance

[billysboat]

Mine is is a 1966 17' Champion speed boat. Kind of heavy in weight and is similar to a Donzi sweet sixteen, wide in front narrow in back. It has a 351 ford motor, a little nicer than stock. Good horsepower, quick response and tuned nicely. It also has Glenwood exhaust thru the transom. The boat was built with and still has the Holman Moody Volvo 280 outdrive and is in good shape.
This boat came with a Volvo 14x22 stainless long hub left hand ultra prop. It revved up nice but was maxing out at about 5400 r.p.m. I then switched to a michigan three blade elephant ear 14x23 long hub left hand aluminun prop. It was maxing out at about 5200 r.p.m. . I recently reworked the aluminum prop and had it cupped. It was nice just at 4800 r.p.m., but would still go to 5000 r.p.m. easily, but then the hub spun.
I'm thinking to go bigger, with like the 15 5/8 23 pitch solas titan long hub left hand stainless. Is this a good idea?

 

[steelespike]

What is the lightly loaded gps speed at 5000? What is the gear ratio? What was the gps speed at 5400 with the 22?
Tachs are always suspect especially if from 66.

 

[billysboat]

The lightly loaded gps speed with the 23 aluminum at 5000 r.p.m was about 47 m.p.h.. It has a 1:61 gear ratio. With the 22 @ 5400, we did not have a gps, but was not as fast.

 

[HT32BSX115]

This boat came with a Volvo 14x22 stainless long hub left hand ultra prop. It revved up nice but was maxing out at about 5400 r.p.m. I then switched to a michigan three blade elephant ear 14x23 long hub left hand aluminun prop. It was maxing out at about 5200 r.p.m. . I recently reworked the aluminum prop and had it cupped. It was nice just at 4800 r.p.m., but would still go to 5000 r.p.m. easily, but then the hub spun.
I'm thinking to go bigger, with like the 15 5/8 23 pitch solas titan long hub left hand stainless. Is this a good idea?

Howdy, Your aluminum prop is likely flexing a bit so any stainless might be good in the same pitch..................The Solas 23 might also be a good try if your tach is correct....... But you MUST ensure that your Tach is accurate and you verify your speedo (or use GPS etc)

Is 5000 RPM the max RPM for that engine?

 

[jester31]

I'd say your tach is wrong,,, With a 23" pitch prop@5000rpm, I'd expect more speed then 47mph? Should be more like 56mph.

 

[billysboat]

I'd say your tach is wrong,,, With a 23" pitch prop@5000rpm, I'd expect more speed then 47mph? Should be more like 56mph.

You may be on to something , I now remember that I found two more holes to lower outdrive down even further. The boat was really moving better and we did not gps it. that is when the prop hub spun on the 23 aluminum. I went ahead and ordered the stainless solas 23 from Iboats. It is one inch bigger in diameter. How many r.p.m. will drop with one inch increase in diameter?

 

[steelespike]

Calculator says 23" @ 5000 13% slip is 58.8 mph. 47 mph with 13% slip indicates about 4000 rpm

 

[jestor68]

Since your original numbers indicate the slippage of a house boat, I'd say your tachometer is suspect.

Using reasonable slip percentage, it shows your rpm at 4300-4400 rpm; not 5000.

Buying props is a waste if the tachometer is off.

If I remember right, those Ford based motors were limited to about 4600 rpm.

The Solas Titan is a "power" prop; not a "speed" prop.