OUTRAGE 18: 20-inch Shaft Outboard - Moderated Discussion Areas

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Author Topic:   OUTRAGE 18: 20-inch Shaft Outboard

WhalerC posted 02-12-2007 02:35 AM ET (US)
Anyone out there running a 20 inch shaft outboard on their 18 Outrage? Will [an OUTRAGE 18] perform correctly with a shorter shaft? The 25-inch shaft motor seems a bit long for shallow water running. Thanks.
Tom W Clark posted 02-12-2007 09:11 AM ET (US)
It does not work that way. Boats that use 25" shaft length outboards have taller transoms that boat that use 20" shaft outboards. The motor's lower unit sticks beneath the keel the same amount on both boats so shallow water clearance is the same.
The only way to use a 20" shaft outboard on an Outrage 18 is to cut a notch in the top of the transom which puts the powerhead closer to the water and allows more water to slop over the transom.
You can use a setback bracket which will allow the motor to be elevated relative to the transom because water will rise back to the surface after it has passed under the hull. The further back the motor is, the higher it can be mounted.
ratherwhalering posted 02-12-2007 01:35 PM ET (US)
I don't think it is practical. With a 12-inch jackplate, water will rise approximately 1-inch behind the transom while on a plane. If you have a high quality, high performance propeller with exceptional cupping, you can run the engine perhaps 2.5-inches higher than the lowest keel point. Theoretically, you would have to adjust the 12-inch jackplate down 1.5 inches from base.
Note however that the powerhead would be closer to the water because (1) the increased transom weight distribution (increased aft displacement) caused by the weight of the engine extended 12-inches from the transon (via the jackplate), and (2) the additional 1.5-inch downward adjustment on the jackplate itself.
In practice, I mounted the same motor (c.1991) with a 25-inch shaft, on an Outrage-18 with a full transom, using a Slidemaster 12-inch jackplate. With a four blade Turbo Propeller (a high quality, high performance propeller with exceptional cupping) we were only able to raise the Jackplate +/- 1.5 inches. You would have to lower it 3.5-inches to achieve the same performance with a 20-inch shaft engine. That's pretty close to the water.

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Author	Topic: OUTRAGE 18: 20-inch Shaft Outboard
WhalerC	posted 02-12-2007 02:35 AM ET (US) Anyone out there running a 20 inch shaft outboard on their 18 Outrage? Will [an OUTRAGE 18] perform correctly with a shorter shaft? The 25-inch shaft motor seems a bit long for shallow water running. Thanks.
Tom W Clark	posted 02-12-2007 09:11 AM ET (US) It does not work that way. Boats that use 25" shaft length outboards have taller transoms that boat that use 20" shaft outboards. The motor's lower unit sticks beneath the keel the same amount on both boats so shallow water clearance is the same. The only way to use a 20" shaft outboard on an Outrage 18 is to cut a notch in the top of the transom which puts the powerhead closer to the water and allows more water to slop over the transom. You can use a setback bracket which will allow the motor to be elevated relative to the transom because water will rise back to the surface after it has passed under the hull. The further back the motor is, the higher it can be mounted.
ratherwhalering	posted 02-12-2007 01:35 PM ET (US) I don't think it is practical. With a 12-inch jackplate, water will rise approximately 1-inch behind the transom while on a plane. If you have a high quality, high performance propeller with exceptional cupping, you can run the engine perhaps 2.5-inches higher than the lowest keel point. Theoretically, you would have to adjust the 12-inch jackplate down 1.5 inches from base. Note however that the powerhead would be closer to the water because (1) the increased transom weight distribution (increased aft displacement) caused by the weight of the engine extended 12-inches from the transon (via the jackplate), and (2) the additional 1.5-inch downward adjustment on the jackplate itself. In practice, I mounted the same motor (c.1991) with a 25-inch shaft, on an Outrage-18 with a full transom, using a Slidemaster 12-inch jackplate. With a four blade Turbo Propeller (a high quality, high performance propeller with exceptional cupping) we were only able to raise the Jackplate +/- 1.5 inches. You would have to lower it 3.5-inches to achieve the same performance with a 20-inch shaft engine. That's pretty close to the water.