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Propheight twin PM 300's

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Old 06-17-2003, 05:55 PM
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Join Date: Oct 2000
Location: Norway
My Boats: Phantom 25 (1985) w/Verado 400R
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Default Propheight twin PM 300's

Hi!

I consider to add another PM 300 on my Phantom 25 offshore hull. The engines will be mounted direct on the transom, 21,5 - 22 inches senterline to senterline.

I have measured from the bottom to the transomedge, and the height is approx. 22,5 inches at each senterline. The transom is a 25 inch.

According to Merc Hi Perf. reccommended propheight is 26 inches at 90 mph with twins measured from the bottom of the boat transom to underside of the outboard transom bracket.

The engines have to be mounted direct on the transom due to the total weight aft. I can not use powerlifts.

The stock midsections are 20 inches, so when mounted all down, the engines heiht will be 22,5 inches. However, further height is limited to 3 inches more due to the mounting holes. So when mounted all up, I will get an engine height of 25,5 inches. Propshaft approx. 2,5 - 3 inches below the bottom.

I do not like to squeeze everything out of the brackets, I broke one straight off two years ago. When mounted all up (lowest mounting holes), the strength will be less.

I can buy aftermarket 15 inches midsections from MadEfi, but then I will get a engine height of 27,5 inches when engine is mounted all down.... Similar to propshaft approx. 0,5 - 1 inch below the bottom....

Conclusion: what kind of propheight should be ok. When running with a single engine and 7,5 inches of setback, the sweet spot is 2 - 2,25 inches below the bottom.

Cheeers, Toffen G
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