Second Time Out, More Problems

[Max...]

Just had a look at your video on the first topic

http://www.rib.net/forum/f36/first-t...ine-67772.html

That transom is cut very low and you have way too much leg in the water, definitely get a raiser block on there.

[kestrel452]

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.

[Max...]

Originally Posted by kestrel452

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:

http://www.rib.net/forum/f50/abc-sib...nes-58373.html

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.

[paintman]

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.

[Fenlander]

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.

[kestrel452]

Originally Posted by Max...

Just had a look at your video on the first topic

http://www.rib.net/forum/f36/first-t...ine-67772.html

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?

[Max...]

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.

[kestrel452]

Originally Posted by Max...

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.

[Max...]

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.

[kestrel452]

Originally Posted by Max...

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....

[kestrel452]

Even though it might not be worth the expense, could a hydrofoil possibly be beneficial?

I am not sure if I have my plate up high enough for it to work properly, though. Or even if a Permatrim plate can be spaced up about an inch to artificially raise it to the keel line.

Here's the clearance I have with the 1-1/4" shim: Imgur Photo Link

[chipko]

Height looks OK, you shouldn't be far off ideal with that.

Just for comparison here is a pic of mine (zodiac also). It's trimmed on hole 3 of 5 which lines the ventilation plate about parallel with the keel line.

[paintman]

Test as you've now got it & see what difference it makes before doing anything else.

[kestrel452]

So I took the Zodiac out for a third time...

I changed the fuel line to a genuine Quicksilver quick connect style line, and replaced the EPA cap on my Attwood tank with a Moeller venting cap (which fit just fine). It was the pre-assembled 8' line with the standard 1/4" thread on one end, and quick connect engine fitting on the other. Had a full tank, and verified that the engine side connector was snapped in place, but the primer bulb just wasn't firming up. Even the crappy Attwood line I had before would firm up pretty quickly after a few squeezes, but this one just wasn't having it. The engine managed to start when i hit the electric starter, though. After leaving the dock and meandering through the no-wake zone to head out, the engine was "sneezing", and continued to do so at times when we were running at less than 1/3 to 1/2 throttle. Could this be caused by a bad bulb????

I also noticed a slight squeal coming from the engine when bringing it down from full throttle that'd last a couple seconds.

The engine should be okay mechanically, I've had it inspected by multiple reputable shops. The only thing that's been done to it recently is the installation of a Permatim hydrofoil (since the inflatable I have it on wasn't planing), and me installing a lower pitch (7 pitch) prop from the stock 9 to bring the RPM's up a little. I sprayed everything with Corrosion X oil, including the thrust washer, spines, prop, shaft spines, and nuts before putting everything on and cranking the prop nut down. I should also note that I'm now using a 1-1/4" white oak shim to get the lower unit up higher.

Any thoughts??? Though the boat seems to be planing just fine now (thank the lord).

EDIT: Just tried squeezing the bulb with the line connected to the tank but not the engine, and it firmed up... Weird....

[kestrel452]

Just as an aside: Does anyone know what the tach pulses per revolution should be set at for this engine to get my Trail Tech TTO portable tach to read correctly? The only choices are 0.5, 1, and 2 PPR.

http://gallery.trailtech.net/media/i...our-manual.pdf

[bartiny]

Each plug will fire (pulse) once per revolution. so if you have the tach wire wrapped arround one plug lead then its setting should be 1.

[kestrel452]

I didn't really mention this in my previous post, but after getting the Permatrim foil, shim, and new 7P prop on there the boat handles WAYYYY more responsively. I was able to get right up on plane, turn on a dime under power (and hold the turn), and get up to 19 mph with two souls on board. I didn't move the fuel tank or any gear forward, I kept everything aft at the stern. I was getting 21 mph with just me on board prior to these add-ons, only a 2mph loss with an extra person on seems like proof enough my performance isn't suffering due to the addition of the hydrofoil.

[paintman]

Would have been interesting to know what difference each extra made.

The 'sneezing' sounds like a misfire so check leads & plugs & I wonder if it's a weak fuel mixture causing it to spit back through the carb.

I have two fuel lines, each with a bulb & have never had a bulb NOT pump up hard providing there was enough fuel in the tank & there were no airleaks at any of the connections or damage to the pick up hose inside the tank.

No idea what the squealing sound is, but squealing noises from engines aren't usually good.