[h4ck3rk1ng]

In any standard frame number designation there are either two or three numbers. Typical examples of frame numbers are 48, 56, 145, and 215. The frame number relates to the “D” dimension (distance from center of shaft to center bottom of mount). For a two digit frame divide the frame number by 16 to arrive at this dimension. For example, in the two-digit 56 frame, the “D” dimension is 3½” (56 divided by 16 = 3½”). For the “D” dimension of a three-digit frame number, consider only the first two digits and use the divisor 4. In frame number 145, for example, the first two digits divided by the constant 4 is equal to the “D” dimension, 14 divided by 4 = 3½”. Similarly, the “D” dimension of a 213 frame motor is 5¼”, 21 divided by 4 = 5¼”.

[The Eternal Coin]

Y indicates that the motor has a special mounting configuration. No details may be assumed regarding this designation. These motors are generally made to manufacturers specifications. These are the hardest motors to find suitable replacements.

[bethel]

D The D flange/face mounted motor. This motor has a special type of mounting flange installed on the shaft end. In the case of the D flange, the flange diameter is larger than the body of the motor and it has clearance holes suitable for mounting bolts to pass through from the back of the motor into threaded holes in the mating part. D flange motors are not as popular as C flange motors. more

[anypromo180]

If your boat has a Transom Height 15"-16" you will need short shaft and if it is 20"-21" you will require long shaft engine. more

[Beelzebuddy]

Auxiliary engines for yachts usually require a long shaft engine so as to make sure the propeller remains well submerged when the boat is in a seaway. [links]

[FreedomFirst]

Small inflatables and dinghies tend to require 'short shaft' engines whilst larger boats usually require long or in some cases special ultra long shaft versions. here

[chyraski]

The correct length for the outboard engine drive shaft is determined by the height of your boat's transom, as measured from top to bottom in the centre. This distance is generally referred to as the “Transom Height” more

[victoriaw]

Propeller selection will depend on your usage. Ski boats need more top end speed, and should choose a prop with a higher pitch. Cruisers and houseboats need more performance at displacement speeds, and should use a prop with a lower pitch to achieve low-end power. It is essential, however, that the WOT r.p.m. falls within the range specified by your engine. If your engine is not able to reach this r.p.m. range, it's operating under an extremely loaded condition.

[pnnac]

The goal in propeller selection is to determine what style and size will maximize your boat's performance, while allowing your engine to operate in the recommended r.p.m. range. The correct propeller will prevent the engine from over-revving, yet allow it to reach the minimum r.p.m. at maximum horsepower.

[billy3321]

If the engine over-revs beyond the maximum recommended r.p.m., you may need to increase the pitch of the propeller. Increasing the pitch increment by 1" will result in approximately a 150-200 r.p.m. reduction at wide open throttle (WOT). If you cannot reach maximum r.p.m. at WOT, then pitch should be decreased. These recommendations apply to single engine installations only. For most twin engine installations it is necessary to increase pitch by 4". Adding diameter will typically decrease rpm, while reducing diameter will raise the rpm.

[betty20a]

-Adding 1 inch of propeller pitch will reduce WOT RPM by 150 to 200 RPM. [links]

[Kline]

Re: Long shaft vs 20 inch shaft motor on Pontoon? here

[huesped]

Another thought I have is to use the 25 inch setup and run a jack plate to adjust the height. There's a lot of water spray out of the back so this might be a way to get the motor up a bit. Dont think I want to run it the full depth and most likely would run it several inches high and it would still be deeper than it is now. I just can't get it any lower the way it is. [links]

[Comatus]

Any input on the number of 20 inch vs 25 inch motors on pontoon boats?

[Mira]

Crb478,
Thanks for the reply. That’s good to know what the norm is because I thought there were more 25 inch motors out there for pontoons. When I had a Pontoon Water Glide under the boat I tried a jack plate (and a motor extension) to lower the motor and I never got the geometry worked out right. It seems the jack plates are more for raising the motor than lowering and the motor had a limited amount that you could tilt it for transport. If there was anyone but me operating the boat I worried about tilting too much and damaging the motor and/or cables. It also sat lower in the water than I liked and flooded out more than once where I had to pull the plugs and pump water out of the motor because of water spray picked up by the motor frame from the bottom and the steering cable from the top. I even built a splash shield to divert water from the bottom of the motor pod so it wouldn’t hit the frame and splash up. I never figured out how to configure a jack plate or motor extension to lower the motor successfully.
I’m running a Power Tech stainless 4 blade prop, 13 inch pitch series RXB4 with ventilation holes in it on an Evinrude 140. It’s advertised for acceleration, holeshot and all around handling. It has a moderate rake and cup. Since I added the third toon and brought the motor back flat against the transom that fixed most of the water spray but I still get some off the steering cable.