Motor Height

[bkerschner70]

So last weekend I got the chance to take my brand new Impact 1850 out on Pool 4. I took the stainless prop off and put on the stock aluminum 19 pitch that came with it (150 Mercury 4 stroke). The boat jumps on plane just fine but as soon as I start to trim it up the prop blows out. The motor is in the 2nd hole down from the top. I was thinking it may be a prop issue but the fact that it blows out so soon makes me think the motor may need to be moved down. Any insight would be great... Without trimming it up I am getting 5,000 rpms and topping out around 39 mph.

[delcecchi]

I guess I would try the stainless prop first. My merc 115 with just a sort of generic aluminum prop, all I ever put on it, would trim up enough to run the boat, but it wasn't very much on the gauge.

When I put on the Suzuki 140, also with regular aluminum prop, it trims up a lot farther according to the gauge, before ventilating. Seems about the same based on the way the boat handles. I''m wondering if the gauges are different, among other things.

[Kyhl]

Curious why you tested it with the aluminum prop.

5,000 RPM is the bottom end of the recommened range for that motor, 5,000-5,800.

I have the same motor on an alumacraft 18' boat (second hole) and depending on prop it runs mid to upper 40's around 5,400rpm.

The fastest I hit was using a Vengeance 19P SS 3 blade at 48mph by the gps.

The Enertia 18P was the slowest at 44mph but it had better grip allowing for a lot more trim and better grip when turning without trimming down much.

My hull doesn't need much trim so I traded the Enertia for a Vengeance 17P and let Jay work his magic, cupped to 18P+ equivalent. Now it does about 46mph @ 5,500rpm and has good grip.

[bkerschner70]

I wasn't sure if there was going to be a lot of debris in the river or not so I thought I'd play it safe and go with the aluminum. I plan on going back this Saturday and will try the stainless before I start adjusting anything.

[Kyhl]

I hear ya. It's always scary testing in the spring. 2 years ago I was on Spring lake shortly after ice out and found a 16 foot long 2X12 board floating in the middle of the lake.

Loaded it up and brought it to a friends dock. That would have ruined someone's day. Guessing it was left behind from an ice house.

[marine_man]

Before I would tweak your hole positioning I'd consider finding a prop that gets you closer to 5800 RPM... see what your stainless does first..

marine_man

[NAMASafetyDirector]

As a quick reference you could trim your motor all the way down and hold a straight edge on the bottom of you hull in the center of the boat and see where it lines up in relation to the bottom of your anti-cavitation plate on the motor. Generally the Anti-cavitation plate should be flush or reasonably close to the bottom of your boat. Slightly above is ok but lower is not. I ran into the same issues last year with my "new to me" boat and found that the motor is sitting about 2" high (or about 1 hole) on the transom.

[boatfixer]

^^^^yup^^^^

5000 trimmed in is prolly gonna be 5500/5600 trimmed out

[ZapBranigan]

Comparing apples to apples Last week I just picked up my Impact 1850 XS with 150 four stroke. I'm in a 2 hr and 10 hr breakin so we are moving between 4500 and 3500 but at 4500 with the std aluminum prop I'm doing well into 43 mph by the GPS with two 200lb guys on board. I have plenty of throttle left but for the first two hrs was told to keep it between 3500 and 4500. So next time out we can wind her up a bit. but I was told 10 hrs of not staying in the same rpm range for extended periods. No long idles or long full throttle. So how new is yours? Oh and just to stay on the apples we are also sitting in the 2nd hole. The prop never blew out of the water. It all seemed to be tuned very well for height. We were set up by R and R Marine out of Shakopee. All the other equipment seems put in flawless.