Prop size for Mac 19?

[Pacamac-uk]

There has been a lot of discussion about prop sizes and WOT in the past, but where did owners of :mac19:s end up?

Magnetic has advised he now has a decent sized engine for his but which propellor diameter and pitch did he go for?

I think mine is standard for the Mercury 40hp 4-stroke. It has 13 x 26 and 2.0:1 on the skeg. Is it really 26" pitch??

Using turningpointpropellors.com prop selector they recommend something around 12 x 10 or 10 x 15. Not sure where I should be heading. It doesn't sound like it's getting to WOT though a 4-stroke does seem less frenetic than a 2-stroke.

Has anyone anything to add to the above?

Cheers

Martin

[magnetic]

Hi there -

The answer is that I don't know the answer, but I might do, just I don't realise it, as follows -

1. I still haven't run my 40hp Merc in the wild yet

2. My engine has a skewed gear ratio (2.0:1 rather than 1.85:1) so I will need to go for a shallower pitch than might otherwise be expected

3. I currently have a 12 inch pitch x 10 7/8 on there - this is almost certainly too big for me, and I currently have an 8 inch on back order from Barrus via Walker Outboards; have a chat with Duncan on 0118 947 8641 - http://www.walkeroutboards.co.uk/ - he seems to be fairly genned up

4. The only real way to go about experimenting is to stick a tacho on the engine and see what revs you get at Wide Open Throttle (WOT); this takes about 10 minutes and £25 -

http://cgi.ebay.co.uk/Tiny-Tach-quartz- ... dZViewItem

I have two of these and I swear by them; I keep them permanently mounted on the front of the hood of each of my engines.

5. I reckon that for a "normal" you would want about a 10 inch prop; as mentioned in (3) above, I'm not normal, but Duncan insists that the shallower the pitch the greater the diameter you need, so I am going for something about 3ft across (maybe useful as a turbine / generator when sailing, you never know.... )

I don't know if this helps much, but remember that the trim (vertical alignment of the prop in the water) and the depth of the cav plate are also critically important. The jackplate I have imported from the US has made fiddling about with these variables far easier and the engine now looks "right" on the boat

In closing, anyone have a view on the Idasailor kick-up rudder system and whether it's available / useful for proper blue-water yachts like the , or just for the fair-weather inland waterways Sunday dinghy sailors ( & )?. Also, any thoughts on quick-release mechanisms which allow the engine to be steered when motoring, but to be decoupled when sailing?

John, where are you when we need you? Beene, what do you know about 's anyhow??????

best regards

Andrew

[Deeseas]

My prop is the orginal that came on the 40hp Tohatsu and it's stamped C12.5 . In the service manuel it states that a C12.5 is 11.3 x 11.5. I don't have a tach but we have done 24.1 mph on GPS about 7 yrs. ago when the motor was a little younger (it's a '93 and has never been in the shop). Last summer we did get up to 22.4 at WOT and we cruise at 16-17 mph, so I believe that it's the right prop for this , motor, and load. I also raise the motor 1" so the cav plate is even with the bottom of the hull and that gave me a little more top end (1 or 2 mph). Hope this helps .
Doug

[Pacamac-uk]

Just realised what 13 x 26 on the skeg is and it ain't the prop size and pitch !! It's the gear ratio, ie 2.0:1 !!

I presume there are markings on the prop but I can't get to it at the moment due to junk stored around the stern of the boat. So I'll have a look when I move the boat a little. Does anyone know what style of marking Mercury use for 'dia x pitch' or is it as simple as that?

(I thought 13 x 26 seemed a bit ambitious for a 40hp outboard, more like the size and pitch on my previous 4hp steam launch. I thought one of you experienced mariners may have known that? Or are you just shy?)

[Highlander]

Ok Guy's

my prop size for my zusi 40hp 4stroke is 11 5/8" x 12 wot is at 5400rpm's , the max for my eng. is 5800rpm's the sweet spot is 5600rpm's so I'm pretty darn close

Cheers John