Merc 80 prop clearance

[floater]

With the Chertsey meet approaching on May 2nd I thought today would be a good day to smoke out the neighbours and fire up the Merc after the winter recess. One of my Christmas presents was a 20 pitch Laser 2 prop so I fitted that but immediately noticed that it clouts the trim tab. Am I doing something wrong e.g. does it need a different thrust washer or do I just need one of those offset trim tabs to set it back from the longer prop?

Incidentally the motor ran great, roll on Chertsey

[se7en]

I don't run a trim tab on JADE, I have an anode without the 'fin', you can cut it off, I doubt you'll notice any difference, If you have time ask puddleduck, he can supply them without the fin ..................................or chop the blades off..!!!

[Rapier]

That'll teach you...

The Flat Earth Society.

[haventaclue]

I'm going to stick my neck out and hope it doesn't get chopped off.I think you are going to find that you are very much over propped.The 20" is what's causing it to clip the tab.
The min -max rpm's on your Merc 80HP are between 4800 and 5200 wide open.Me thinks,unless the Shakey is very light,you will be hard pushed to get up to 4800rpm's,and that will put strain on the engine.
I have a two blade aluminium 13.25x19" which I run on "NO-KIT" when I'm on my own and it pushes up to 5300rpm's,a wee bit over.When I have the girls on,I run a three blade aluminium 13.25x17" which just makes it to 5100rpm's.The three blade 19" pitch will only push up to 4900rpm's with four on board.
Another consideration is the s/s is stiffer than aluminium and needs less pitch to reach the recommended rpm's.
So as it was a Christmas present, get one of those Yamaha offset trim tabs.

[se7en]

Floaters 80 is the later ADI motor, with the extra transfer port, it will rev to 5600-5800, its the same block as my 850XS, the rake on the blades is for bow lift, its nothing to do with pitch, with this on his boat he should be able to lift the engine and run it high, this will also help it to get its revs up, the square vent ports in the front of the hub at the root of the blades will help as well, may take a bit of messing about but he should be able to pull 20" pitch.

[se7en]

Another view. We run it around 4" high.

[floater]

Thanks for the replies. I saw the post from Haventaclue so went for a rummage in the garage to find my 21p ally prop and compare it to the 19 ally. Having now returned I see that Se7en has replied. My comparison showed that standing the props side by side vertically on the inner hub surface the blades end at exactly the same height. The laser is a longer prop overall probably designed that way for good reasons.

I have been running a 19 ally prop with no problem, we did a bit of waterskiing last summer and had the boat loaded with fuel bow and stern at Hayling. Part of my tinkering today was to calibrate the rev counter using my hand held tacho directly on the crankshaft in prepetration for some proper evaluation at Chertsey (sans trim tab)

[Alacrity]

I have laser 2 on my Merc 115 & like Se7en does, I run a flat anode with no tab on it. HOWEVER I have hydraulic steering so I don't need it to compensate engine torque. On my Broom I had the 650 offset so she ran straight 'hands off' which made her nicer to drive. If you are not bothered about this then run a flat anode, if you want to neutralise the torque get a tab with the rear offset to clear the prop & set the offset.

[solitaire]

Solitaire has a cut off Anode and I think you have been out with her! - and no torque steer effect - (straight as a arrow ) -If yours does steer to one side try a case of beer on the opposite side -then you can fine tune it by offloading the beer to other members boats

[floater]

I have a teleflex no feedback helm so trim shouldn't be a problem