I'm rigging a 2000 Pulsare BRX with a 20" 225 Promax wearing a sportmaster gearcase mounted to a cmc 5.5" jackplate. When I asked the rigger to set the motor height so that the propshaft centerline is 3.5" below the pad he looked at me like I was out of my mind. He advised me that the cavitation plate should be even with the pad or the motor would constantly blow out. Any thoughts?
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Cavitation plate height
- Thread starter Lestat
- Start date
karzrus
Well-known member
Best advice I have been given and have for you,
When you have a jack plate, you want the top of the travel to finish with the prop centreline flush with the bottom of the boat.
If your set back was in the 12-16" range like some have, you might even want an inch or two of travel above the bottom.
When you have a jack plate, you want the top of the travel to finish with the prop centreline flush with the bottom of the boat.
If your set back was in the 12-16" range like some have, you might even want an inch or two of travel above the bottom.
100% correct for our V-bottoms.
Lestat, your rigger/dealer is like most, clueless when it comes to rigging faster boats. I've got my prop shaft at 4" below the pad right now, going back to 3.5" this weekend. My boat is used for tubing at 22 mph, so deeper is better.
Lower unit blow out is a result of speed, not motor height. If the rigger referred to cavitation as blow out, it suggests the rigger doesn't know much about high performance outboards. With your boat, motor, and gearcase you're never going to get to blow out speeds (excess of 85 MPH) so I wouldn't worry about that. Furthermore, you've got a Sportmaster which people have taken up to 120 MPH without blow out.
I had a similar setup on my 2000 BRX for one weekend. I had a 2.5L Merc with 20" mid and CLE gearcase on the factory 5.5" CMC jack plate. Based on that, if you're trying to figure out what bolt holes to use on the motor clamp, my suggestion is to get the motor as high on the jack plate as you can. In other words, use the bottom holes on the motor's bracket to bolt it to the jack plate. The factory transom bolts on the 2000 BRX are very low to accommodate the motor splash well, and this causes the motor to sit way deeper in the water than you'd ever need it. If you bolt the motor to the jack plate using the bottom holes and put the jack plate around the middle of it's vertical travel it should run well for general all-around boating while giving you the option to adjust the jack plate down or up from there depending what you want to do. If you put the jack palte within an inch of the top of its travel it will cavitate on takeoff, but assuming you don't have too much weight on board you can feather the throttle and still get on plane for when you want to do a bunch of high speed runs. With your setup I figure you'll see 70 MPH without too much trouble.
Hope that helps.
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Another thought for you. If you want to keep it simple for your rigger and minimize any pushback you might get from him, maybe just tell him to bolt the motor to the jack plate using the bottom holes on the motor bracket and put the CMC jack plate all the way down as far as it will go. Then when you get it home you can raise the jack plate yourself.
I have my propshaft adjusted to 3.25" below the pad now. It runs real well when not towing, hoping to test this adjustment while towing tubes today.
Here's a pic that you can show your rigger. I took this pic so you can see how high the clamp bracket is above the 1850 transom lip.
Here's a pic that you can show your rigger. I took this pic so you can see how high the clamp bracket is above the 1850 transom lip.
