VP 250a 270 OD- what prop for betterpower/speed

I have acquired a Bayliner Trophy 2160 Cuddy - Originally had the 131 @ 125hp. Was rated for 125-225 hp engines. Engine needed replacement (block holed). Owner not well and moving needed to clear out sold property - instant "free" boat ownership.

Not a mechanic nor even a boat DIY'er except for sanding, painting rewiring trailer and such. Have run a Chryler Courier trihull, bowrider, with original evinrude ob for a few years. My Dad was a light house keeper so ran out with him when very young but little ownership experience. Have been reading a lot about Pentas - but speak simpleton to me please.

I have acquired and it is in the process of installation a VP 250a 148hp. Using same 270 od. With old engine prev owner said - very difficult to make plane. Figured this would be enough 148hp would do better - no transom mod needed.

Looking for ways to get a bit more out of it. Will be on the Chesapeake Bay. Summary 21'6" boat, 4cyl 148 hp dual carb, single prop 270 outdrive. What prop change or other mod would give more juice?

Please remember speak simpleton.

The (typically) one and only prop size is that prop that allows the engine to rev up to WITHIN the specified maximum wide open throttle RPM range with:
Properly tuned engine
Tank 3/4 filled (at least) with fresh gas
clean bottom
normal load of gear and number of passengers
calm seas, low to no wind.

I'd start with the same prop P/O had on engine as a first trial (assuming its in good shape) and go from there, i.e. if engine won't rev up to the minimum specified RPM, go to a prop with less pitch, if it over revs go to a prop with more pitch . Props are specified by diameter and pitch, wherein a 14x13 prop is a 14 inch diameter prop with a 13 inch pitch where pitch is defined as the distance the prop will move the boat if it was 100% efficient, i.e. no "slip". Aluminum props are the best overall props for "normal" boat owners.

Thanks. This has a 60 gal long range tank - would you still fill it 3/4 (45 gal)? 30 gallons would probably last me a good amount of water time.
Would the 270 have been fitted with a different prop if originally paired with the 250a rather than the AQ131?

Kathy said:

This has a 60 gal long range tank - would you still fill it 3/4 (45 gal)? 30 gallons would probably last me a good amount of water time.

Would the 270 have been fitted with a different prop if originally paired with the 250a rather than the AQ131?

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As a general rule and safety measure (regarding the amount of fuel): Plan your trips so that you use approx 1/3 out, 1/3 back, keeping 1/3 in reserve.

Both of those OHC 4's require the 2.15:1 final gear reduction.
Remove the prop, remove the ring anode and wire brush the AFT surface of the prop shaft bearing carrier.
The reduction will be stamped into the carrier and should read 2.15.

The AQ250 will easily turn the same prop that was fitted with the AQ131.

As Bob suggested, in order to find out if a prop is correct for your application, you will need to perform the WOT RPM test to see if the engine can achieve the specified WOT RPM. Engine in full tune, hull clean, boat loaded as you would normally, etc.

See your OEM manual for the specified WOT RPM.

Keep in mind that the OEM WOT RPM is a test RPM only. You will NOT be cruising at this RPM, unless you wish to shorten the life of your engine.



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Thanks Guys
Hull has been sanded and bottom painted, plugs. points, new plug wires etc. Most of the boat wiring has been replaced because someone jury rigged a lot. Gas tank drained and fresh filled - lines replaced. So once they finish with the 270 remount it will be test ready!

[FONT=&quot]I looked at the manuals as you both recommended. They had only two standard configurations. With the AQ131/270D they had a 15 x 17 prop. With a AQ 225d/280D they had a 15 x19 prop. I have an 250A/270D. The 125 was 131 HP. The prop is, I assume, the original - white, aluminum 15X17. Will measure when I can get to it. Using the 250a engine what change would you be expecting in these specs?

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Kathy said:

I looked at the manuals as you both recommended. They had only two standard configurations. With the AQ131/270D they had a 15 x 17 prop. With a AQ 225d/280D they had a 15 x19 prop. I have an 250A/270D. The 125 was 131 HP. The prop is, I assume, the original - white, aluminum 15X17. Will measure when I can get to it. Using the 250a engine what change would you be expecting in these specs?

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Kathy, first off, we cannot fairly compare the AQ131 w/ a 270 drive reduction (2.15:1) with the AQ225 w/ a 280 reduction (1.61:1) when attempting to figure out a prop pitch/diameter. The dynamics are completely different.


Secondly, there is no substitute for the WOT RPM test, of which means that you will need to try several different propellers!
Some prop shops will let you borrow several different propellers for this test!

Since the boat was likely over propped by the P/O ( in an attempt to get more speed) and you now have a larger engine... as stated above, existing prop a good starting point. While one can reasonably "measure" a prop's diameter, determination of the pitch is beyond most boat owner's capability and is best done by a prop rebuilding shop as it requires special tools. A used prop should always be sent to a good prop shop for a "rebuild" anyway. Try to find the P/N or possibly the Diameter and Pitch stamped in the metal of the prop.

sandkicker said:

While one can reasonably "measure" a prop's diameter, determination of the pitch is beyond most boat owner's capability and is best done by a prop rebuilding shop as it requires special tools. .

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Bob, this is very simple.
Go to the store and buy all of the Jello that they have.
Plan on spending $75 or more.
Cook the Jello in a 55 gallon drum with one side cut open and laying on its side.
Put the prop into the jello and let it cool.
Turn the prop one revolution, and then measure the distance that it traveled.
See.... I told you how simple this is....... LOL



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thanks. Learning a lot.

Kathy said:

thanks. Learning a lot.

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About props, or about the different uses for Jello?

New uses for jello are always fun. But I have been reading archives about seals and ratios and ... Trying not to be too much of a dummy before I start going out in this boat. I like the older boats but want it to be reliable and relaxing. Ya never know enough. Better prepared is more relaxing and fun. The bay is great for exploring creeks and coves and watching the wildlife. I enjoy that in the 15' but if any kind of real breeze comes up the ride goes from rough to brutal quickly. So this boat will let me do all sorts of things I could not do in my Chrysler. Go Further in different wind condition, The Chrysler moved like a bat out of hell so I will miss that but this should be a big improvement. Semi retirement lets me go out on weekdays so I can avoid the insane # of sail folks that are out on the weekend around here.