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Old 06-01-2015, 01:18 AM   #1
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Default Need advice on our new boat

Hi Yall. I have been watching the forum for a while and just bought a 2004 maxum 1800 mx. We took it out the other day and love it! It has a mercruiser 3.0 with the alpha 1 drive. What I noticed is that I got to 5400 rpms at 41 miles per hour. I immediately reduced speed. At 4500 rpm it was only 36 mph. The prop the previous owner put on it is an aluminum 4 blade 19 pitch. We will be pulling the kids on a tube some. Can you all recommend a different prop to lower wot? What props are Yall running on the same boat. I am looking at a stainless 14.25 dia with 21 pitch. Also, when we plane out if I raise the trim just above the 3/4 line it starts revving. Is that normal. It seems we really have to leave the trim really low. Thanks
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Old 06-01-2015, 03:43 AM   #2
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Welcome aboard.

On the run where you hit 5400 rpm were the kids onboard? Also gear that will be part of a normal trip?

Mercruiser has a prop calculator on the site.

How are you triming the drive to get it 3/4 up? The trailer button should not be used.
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Old 06-01-2015, 12:34 PM   #3
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I have a 2001 1800 with the 3.0. For watersports/tubing I get best performance with the drive trimmed down between 3/4 and full down using a 17 pitch prop. Weight is evenly distributed in the boat and I am using the standard tow hook in the back. I am usually close to max weight.
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Old 06-01-2015, 02:47 PM   #4
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Quote:
Originally Posted by jrsick View Post
I have a 2001 1800 with the 3.0. For watersports/tubing I get best performance with the drive trimmed down between 3/4 and full down using a 17 pitch prop. Weight is evenly distributed in the boat and I am using the standard tow hook in the back. I am usually close to max weight.
Not enough information here. 'Best Performance' is subjective. There is no indication of what the max RPM range you're getting is here. The diameter and number of blades of the prop is not listed either, only the pitch. Nor is there is indication of your goal.

A boat setup to pull a slalom skier out of the water is more than likely going to be under-propped.

https://www.mercurymarine.com/en/us/...or/#/step-five

With more information you can get the prop calculator to dial in the recommendation closer.
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Old 06-01-2015, 08:35 PM   #5
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The boat is 1900+/- lbs. The boat is rated for 900lbs. of people and gear. When we went out we had 750+/- lbs. and did not pull skiiers. I think I wrote the trim comments wrong. I meant that I started all the way down and raised the trim 1.4 to the hash mark (3/4 down). Previously, I thought that, on plane, the trim should be around 1/2 down or horizontal. I see that jrsick stated that he runs the trim 3/4 down on plane, so that makes me feel better. I did the prop finder and it came back with 6-7 props, all being 20-21 pitch so I thin that is what I might go with.

Just curious, but is there a rev limiter or adjustment that should be made to the carburetor or motor that limits the RPMS? Or is the RPM strictly based upon the prop? Thanks for all the advise.
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Old 06-01-2015, 09:58 PM   #6
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A carb engine does not have a rev limiter.
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