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I finally got the chance to look over the stern at speed today and take a picture. It's rather low quality because I used my cell phone camera, but you can clearly see that my cav plate is buried. This was at 28 - 30 mph with an appropriate amount of positive trim. My motor is mounted at the center hole (out of 5). Judging by the photo, that's obviously too low. Will raising it up reduce smooth water porpoising?

Thanks,
Ric

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What motor are you running. I would raise it up until it breaks loose in rough water, or rapid acceleration. Should be about 1/2" to 1" above the bottom. Motor height really isn`t a factor in porpoising. Moving your whole interior forward 6" will just about eliminate porpoising in the 13 footer Unfortunately your steering cable may now be too short. . Also mount your gas tanks under the rear thwart or better still the front thwart. Mount the battery under the rear thwart. You will have to mount the thwart on top of the seat clamp to do this, but its more comfortable to drive in this position anyway.

rich

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I have a 2001 Sport 13 with the mercury 40 HP 2 stroke. It has 3 holes and was set up by the dealer with the motor as low as it could go. After playing around I ended up with a 10-3/8" prop with a 13 pitch. I also found it runs best with the motor as high as it can go on the mountings.

Three adults can run up on plane with no problem. It can also do it with four, but they must be average or less build. I can get up on plane with five, only if at least two are young kids. This is with full fuel, anchor in the stowage locker and other equipment on board.

I always get porpoising when I tilt up for speed. That's the limiting factor. I have heard a Stingray or other stabilizer can improve on this. The reports are generally good but some are contradictions to this.

You've got a fun boat. I wish there were others aroud my home.

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Your cavitation plate needs to be even with the keel.

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John -

Can you explain your divergent opinion?

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John, I believe your opinion is old school. proven not true.

rich

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So where should the cavitation plate be in relation to the keel? I've heard that while under way, you should be able to clearly see the cavitation plate.

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Take a look at this. Somebody sent it to me before I worked on mine.

http://www.veradoclub.com/smf/index.php?topic=137.0

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Generally speaking it should never be lower than the keel.

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Great stuff Burtim!! I think I'll need to raise my motor a notch.....I cannot see my cavitation plate at all when I am at cruise.

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This photo is running at WOT, 6000 rpm, fully trimmed out on my 2008 130 Sport; stock 14P aluminum prop. The motor has been moved up one hole from the factory mounting so it is one hole down from the highest possible mounting. With the trim tucked all the way under, the AV plate is about 1/4 - 1/2" above the keel. The tell-tale is squirting an uninterrupted stream of water so the cooling must be okay. No ventilation in sharp turns. When I tested the boat with the motor at the highest mounting, the prop would slip in sharp turns unless the trim was fully tucked-in. In reality, the boat would probably perform better at the highest setting but the Boston Whaler rep I was talking to last week was having a cow about the fact that I'd moved it up two holes.

Next step is to figure out which SS prop to put on . . . waiting for Tom to get to get back from his wedding . . . what an inconvenience. :D

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This one is at 5200 with an "appropriate" level of trim for the speed. Not the best picture angle . . . sorry. But the AV plate is right below the surface.

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Ric,

It's my understanding that when you go to the stainless prop, you may well be able to raise it that last hole with no slippage at all as the stainless have far more grip and holding power than the aluminum. It's well worth a try when you get the new stainless on there...

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Maybe I missed it but I still don`t know what HP and brand of motor your running. By your pitch that you stated I am surmising it is a 4 stroke 40.
rich

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You have surmised correctly. B)

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Yes, this can be true for a couple of reasons. Alum props are more likely to have damage or imperfections in them which can promote slippage. Also, SS props have cupped blades more often than aluminum. Unfortunately, my only 3-blade option in Mercury props is a Vengeance which has no (or very little) cupping. I'm also considering a Trophy Sport 4-blade. Not sure if it is cupped but it's less of an issue since 4-blades already provide more grip.

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My 130 Sport has its 4 stroke 40hp Merc in the center hole out of five. I think raising it would not be right for my choppy bay, which has a large amount of two and three foot boat wakes sneaking up on you from time to time. My issue was not how to get more speed out of my set up, but rather how to get it to plane at a slower speed.

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As a result of this thread, I've raised my engine up about an inch on the transom. Now, when I am WOT, I can see the cavitation plate whereas I could not before. I think I may be getting anout 1 knot more in performance but at least I know the set-up is correct now.

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I forgot to mention, one of the nice benefits of moving the motor up is reduced steering effort.

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I have one more hole to go on my 22' Outrage but am hoping that the new stainless prop may give me the needed stern lift so that it won't be necessary to go up that last hole. I realize your selection of ss props is much more limited for the 40 hp, and I don't know if the same rules would apply for the smaller engines, but that may be a surprising benefit when you get the new stainless on there... Interesting thread, looking forward to seeing your results!

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Dave, what kind of SS prop are you considering? You may already know this but generally speaking, the straighter the trailing edge of the blades (vs rounded), the more stern lift you get. Rounded trailing edges (and a high rake angle) generate more bow lift.

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I'm going to try the Mercury MiragePLUS prop Ric as I've been told that large blade, low rake props have more stern lift ablilty. Hadn't heard that about the trailing edge though... There's a Raker on there now and it sure does lift the bow (and push the stern down), making it difficult to achieve lower rpm/speed plane, which is also negatively impacting fuel economy.

Getting this new Etec has been a real education in the importance of selecting the correct prop, and I'm amazed dealers don't pay much more attention as it can really enhance or more importantly detract from a new installation.

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Dave,

Dealers don't have the time, patience and often not an adequate understanding to really prop a boat right. Anyway, my previous boat (a high-powered Baja) had a Mirage Plus. Great prop, but I don't think I agree that it is a low-rake, stern lifting prop. But you may not need as much stern lift as you think, and the Raker is clearly a high-rake prop. Take a look at this website:

www.hydromotive.com/propellers.html

Look at their descriptions of the Quad IV (stern-lifting) and Quad IV-X (bow-lifting). I'm not recommending these props for your boat. It's just a good site to read about the effects of different blade designs. At the end of the day, a Mirage Plus may very well be the best bet for you.