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Old 17 May 2015, 18:00   #21
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Just had a look at your video on the first topic

First Time out with the Zodiac, Major Problems with the Engine...

That transom is cut very low and you have way too much leg in the water, definitely get a raiser block on there.
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Old 17 May 2015, 21:46   #22
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I'll have to take a second look and see if it could benefit from a shim, I'm not sure but last time I checked the cavitation plate + keel alignment it was satisfactory. Not certain if a shim would even help planing, though.

To those more experienced: Would adding a lower pitch or 4-blade prop, and installing a Permatrim hydrofoil help get me on plane? According to the marina I brought it to, I have a 9 x 9 stock prop. Maybe putting a 4 blade on there would be better than simply a lower pitch 3-blade???

Though some reading has created confusion with regards to the switch from a 3 to 4-blade prop. Apparently to keep RPM parity, you have to drop a pitch or two when going to a 4-blade. Assuming my logical change in pitch would be down two inches from 9 to 7 if buying a 3-blade, what pitch 4-blade would I be looking at? If a 7 pitch 4-blade has the same RPM parity as a 9 pitch 3-blade, would that mean I'd have to go to an even lower pitch 4-blade to gain higher thrust?? Is the assertion that 4-blade props are more meant for thrust as compared to 3-bladed props even true or significant? I have no problem buying one or two extra props to experiment with.
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Old 18 May 2015, 02:39   #23
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Originally Posted by kestrel452 View Post
I'll have to take a second look and see if it could benefit from a shim, I'm not sure but last time I checked the cavitation plate + keel alignment it was satisfactory. Not certain if a shim would even help planing, though.

To those more experienced: Would adding a lower pitch or 4-blade prop, and installing a Permatrim hydrofoil help get me on plane?
No, but getting the height right will help a little with top speed.

Well worth reading through this very detailed guide:

ABC Sib-Rib Installation Guidelines.-

However, and apologies for sounding like a stuck record but all these points (incl prop changes and adding hydrofoils) are tinkering round the edges and dealing with the symptoms - as many have repeatedly said on here you have one very fundamental problem - an underpowered and overweight rig.

Lose weight or add (significant) power is the simple answer.
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Old 18 May 2015, 03:38   #24
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Permatrim means I get onto and stay on plane at lower speed - so better economy - BUT the boat would get up on the plane anyway. Permatrim is a big alloy plate, not the little fin things.
I also re-propped from a 19 to a 21. Again, economy. The 19 would probably be better for pulling skiers - better 'hole shot' - but I don't do that. Stays within the engine manufacturer's recommended WOT rev range. I tried a 23 but it wasn't suitable.
You could try dropping to a 7 or trying a 4-blade (I have no experience of those), but unless you can borrow them you risk spending a fair bit of money for no result.

Have you tried one of the on-line prop calculators - such as Mercury's own - to see what's recommended for your set-up?

Have a read through this: http://solas.com/newweb/propeller/tech/basic.asp

ETA Bear in mind that the pitch of a prop refers to the distance it theoretically travels for one revolution so the smaller the number the less distance it will travel - so you will lose some top speed. That may be an issue for you going on your posts so far.
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Old 18 May 2015, 04:14   #25
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Max is right... it's the weight... whatever tinkering you do the load you're asking this SIB to carry will always make it unresponsive.

However if you wanted to try a 4-blade then yes you do have to take the pitch down but I wouldn't add the drop you might have tried if you just dropped pitch on another 3 blade. I think going down from 9 to 6 is too much so try a 7 or 8 4-blade.

The 4 blade props are made to cope with a greater load but they are often (with a planing craft) on a much more powerful outboard, they do have greater drag offsetting their greater theoretical thrust. Beware there are 4-bladed props with a profile really only suited to heavy displacement craft and these types could actually create more problems.
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Old 18 May 2015, 16:01   #26
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Originally Posted by Max... View Post
Just had a look at your video on the first topic

First Time out with the Zodiac, Major Problems with the Engine...

That transom is cut very low and you have way too much leg in the water, definitely get a raiser block on there.
I inflated the boat to investigate your claim. I think you are right. I measured around a 2" difference between the ventilation plate and keel.

Please take a look at these photos. The engine is fully down trimmed.

*Imgur Photo Link*

Could such a deviation cause some loss in performance?
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Old 18 May 2015, 16:28   #27
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Only very minor (ie 1/2 to 1 knot or so maybe at WOT) at this level but check the Locozodiac link and do it on the water as load affects it.
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Old 18 May 2015, 18:23   #28
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Only very minor (ie 1/2 to 1 knot or so maybe at WOT) at this level but check the Locozodiac link and do it on the water as load affects it.
Well, raising the motor two inches would lead to the clamps no longer being flush on the inside metal plate. I'd need to install a Mini-Jacker, or similar transom riser. Doing so would probably cost me about $200 all said and done.

I'd need to get it raised though if I ever plan to mount a hydrofoil, if my plate is buried 2" the foil won't come up out of the water and just drag on the boat. Probably looking at $400 total including parts... No idea if it's even worth messing with.
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Old 18 May 2015, 18:31   #29
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I'd just raise it with a small wooden batten Sikaflexed to the top of the transom that just leaves the clamps in the right place, you might have to compromise on 1" say. Anything else is not worth the hassle/expense.

Once again though and as per post linking Locos topic above do all this *on the water*. Raise it too much and you might find it cavitating too easily on the turns so you need to get that tiny tach and some varying thickness battens and do some experimenting.
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Old 18 May 2015, 20:12   #30
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I'd just raise it with a small wooden batten Sikaflexed to the top of the transom that just leaves the clamps in the right place, you might have to compromise on 1" say. Anything else is not worth the hassle/expense.

Once again though and as per post linking Locos topic above do all this *on the water*. Raise it too much and you might find it cavitating too easily on the turns so you need to get that tiny tach and some varying thickness battens and do some experimenting.
Good advice. I can raise the motor 1-1/4" without necessitating modification to the boat. I just lifted the motor up as far as the circular clamp pads would go until they hit the lip of the metal transom plate. It gets it *about* right, still a hair below the keel, but that last 1/2" isn't nearly worth investing $200-300 of parts/labor. I bought a Trail Tech tach, and will retest the boat with the shim and 7 pitch prop hopefully this holiday weekend. Crossing my fingers this will make a good difference in planability....
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