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steffanf

Couple questions about props and pitches

12 posts in this topic

I have a new Lund 1425 Classic which had a Merc. 30 4-stroke. The prop pitch was an 11. It ran fine and got on plane rather quick with one person and gear. Speed was estimated at about 25-30 mph. When one other person was added, it was a DOG! It would not get on plane and only ran about 15 mph. I was told by the dealer to switch to a 9 pitch, but that my top speed would suffer badly. I really didn't want to loose any top speed, since it is not a real fast boat anyway. I'm not sure what was wrong here, but perhaps someone can fill me in on what's going on.

I didn't try the 9 pitch on the 30... and instead decided to upgrade to a Merc. 40 4-stroke (max HP allowed on this boat). I haven't tried it yet, but the pitch on the prop is a 13. Am I going to run into the same problem I had before? Should I go ahead and get an 11 pitch right off the bat (to swap out when at the lake) before even trying it, or will the extra 10 HP cure all my problems?

-Gregg B.

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If you moved more weight to the bow, the boat would plane with the 30.

Heres an example but more of an extreme. If I put a 10 hp on a 12' boat and left the gas tank in the stern with just me in the boat the boat will not plane out. If I move the gas tank to the middle of the boat the boat will plane out and top speed will be close to 30 mph. Whats going on is you can only push something through the water so fast. A boat at some point must stop plowing water and get on top the water. It needs help. Weight distribution with a smaller boat and motor is the most important factor. With the same boat you can overcome weight distribution with more Horse Power only if you add trim.

Will the 40 hp over come that transfer from plowing water to plane by using the trim if you ignore weight distribution?

Yes it will. You should more concerned about being proped right at WOT RPMs though. If that means moving weight forward to improve hole shot then you should do that.

As far as the pitch you have now, you'll have to see what the RPMs are at WOT.

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EFI right?. Take the other prop along anyway. It's hard to say. You will add about 45 lbs, but have 10 more hp (25% increase in this case), and the 40 has a slightly lower gear ratio. Keep in mind what Frank says though about max rpm at WOT. You don't want to over rev this thing.

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Here's a couple things I should add. Both the 30 and 40 are EFI engines (2007 models). The boat has power trim and is actually a 1425 SS with a console. I do not have a tachometer, but I would have to say that the boat was not reaching full RPM's (just guessing by sound) with 2 people in the boat. As far as weight distribution goes, I sent the other person to the sit on the floor of the bow of the boat to see if the performance was better. I noticed very little change in performance. I tried different trim settings, finding the best performance (at 15 mph) was attained with the motor trimmed all the way in (down).

Now, with the 40 installed, I do not have another prop to test. I still haven't even tested the boat and motor yet since I swapped out the motor. Since the new 40 HP motor comes with a 13 pitch prop, I was thinking of buying another different pitch prop so I can test it at the lake when I go out this Sunday. If any problems with getting the boat on plane should occur, I would assume I might need to get a lower pitch prop. Should I get an 11 pitch or a 12 pitch to try?

-Gregg B.

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I would try an 11 pitch prop.

It seems odd that the best performance came from having the motor all the way down though.

marine_man

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Console and guy in the bow. Totally ignore my previous post but those with that type set up keep it in mind.

A tilt and trim on a 30 is not going to make that much difference. The 40 however with T&T will make you boat act like a different animal. I wouldn't buy a new prop till you get it on the water. About the console and estimating RPMs, its impossible. A tiller with an experienced boatmen yes but it gets harder when your not next to the engine.

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Well, I am going to test drive the boat with the new 40 HP this coming Sunday. Since it will be on a Sunday, when most dealers are closed, and I would like to see just how well this thing runs, I decided to purchase a couple extra props. The place I bought them from will let me return one or both of them if neither of them work for me. Right now, the stock prop is a 13 pitch, so I got a 12 pitch and and an 11 pitch to try out if the 13 doesn't cut it. Any other words of wisdom? If not, I will post my results here next week and let you know what conclusions I made.

-Gregg B.

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Good Luck!

Here's some advice: stay away from the rocks smile

Also try and stay away from the sand - if you're trying a prop you don't end up buying and you sand blast it from running in sand they may not give you your money back.

marine_man

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Well, I haven't tried out the other props yet. The brand new 40 HP Merc the dealer installed actually blew a fuse. The replacement fuse blew right away and they have since found out that the ignition and wiring harness now needs to be replaced. All these problems are starting to get me sick... and I feed the dealer really doesn't know what they are doing or talking about. I should have the boat back this Friday... and it BETTER be fixed! I will then let you all know what I find out about the prop situation (unless something else goes wrong).

-Gregg B.

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OK... all is well. The new 40 HP has been repaired and I finally got to test it on Friday. It works just fine getting up on plane and speed (probably close to 30 mph) with 2 people in the boat. You guys were right about the 40 HP being a totally different motor compared to the 30 HP... the power difference is VERY noticeable. I tested it using the stock 13 pitch prop that came with the motor. It certainly doesn't need a lower pitch prop I didn't even try the 11 & 12 pitch props I have. I will just return them where I bought them, exchanging them for a 13 or 14 next week.

-Gregg B.

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Yeah... all's good now. I'm going to return the props on Friday. I'm thinking I should exchange them for a 14 pitch... just in case even more speed is attainable. I don't know... maybe I'll just get another 13 for a spare...

-Gregg B.

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