Prop question

[Chamelion]

Hi there,

I have a Quintrex Dory 4.1m wide body, Mercury 967cc 40hp (detuned 60hp) and I feel she may be running a less than ideal prop.

At the moment it has:

48 846702A40 12p

10-3/4” 12”p
3blade Alum
1500-2500lb recomended boat weight
15-19’ (feet long) boat length
18-27mph max speed

That's straight out of the motors workshop manual.... Does that appear to be the wrong prop for my boat? Should I be looking at something else as per below... At the moment I've hot brilliant holeshot and she'll max out at a slide over 50km/h. Adding another adult and two kids to the boat doesn't appear to change the holeshot and I lose about 5km/h off the top speed.

Certainly prepared to consider changing props if I have the 'wrong one'.

Cheers.

http://i225.photobucket.com/albums/dd46/Chamelion/props_zps61188938.jpg

[Kero]

Why not give Troy Wood (from Seaquest Performance) a call, they are Merc dealers who are getting great feedback on here! Troy is a member on Ausfish.

[Fed]

Get a tacho mate it's the only way to be sure.

[Moonlighter]

The only way to tell for certain is to check engine rpm at full throttle. You need to get close to the max recommended rpm for your engine.

Having said that, if as you say your hole shot is great and you get 50km/hr flat stick, then I think you will be pretty close to where you should be. I wouldn't expect more top end from that hull and motor. Sounds pretty good to me.

What makes you think you could have the wrong prop???

Usually if you have the wrong prop, people complain about crook/doughy hole shot or low top end speed, neither of which you seem to have.....?

So what problems/symptoms is your boat exhibiting that make you think the prop is wrong??

Forget that table, it's just a rough guide. Pretty meaningless in real life.

Cheers

ML

[Lightly Toasted]

I have the Tohatsu built 40HP Merc (3cyl) which runs a 11.4X12 prop and does around 50km/h on a 4.4m SeaJay.

I think you're in the speed range for that motor, but as Fed & Moonlighter said; pick up a tacho and check what your RPM's are doing. That's the only way you'll know.



Rob.

[fisho8]

Why not give Troy Wood (from Seaquest Performance) a call, they are Merc dealers who are getting great feedback on here! Troy is a member on Ausfish.

X2 I just got a new prop on my boat through them Troy will be able to point you in the right direction.

[Chamelion]

Why not give Troy Wood (from Seaquest Performance) a call, they are Merc dealers who are getting great feedback on here! Troy is a member on Ausfish.

Cheers, will look into it. Was also going to contact solas and maybe also price up a SS prop.


Get a tacho mate it's the only way to be sure.

Any recommendations on a cheapish tacho?


The only way to tell for certain is to check engine rpm at full throttle. You need to get close to the max recommended rpm for your engine.

Having said that, if as you say your hole shot is great and you get 50km/hr flat stick, then I think you will be pretty close to where you should be. I wouldn't expect more top end from that hull and motor. Sounds pretty good to me.

What makes you think you could have the wrong prop???

Usually if you have the wrong prop, people complain about crook/doughy hole shot or low top end speed, neither of which you seem to have.....?

So what problems/symptoms is your boat exhibiting that make you think the prop is wrong??

Forget that table, it's just a rough guide. Pretty meaningless in real life.

Cheers

ML

No problems really.. I do have prop chatter that's very noticeable at low revs/low speed. As I said, hole shot is fine and max speed certainly isn't a problem. But I wouldn't mind trading some of that hole shot for some better cruising and max speed.

The prop is also fairly ordinary condition wise, see pic below.


I have the Tohatsu built 40HP Merc (3cyl) which runs a 11.4X12 prop and does around 50km/h on a 4.4m SeaJay.

I think you're in the speed range for that motor, but as Fed & Moonlighter said; pick up a tacho and check what your RPM's are doing. That's the only way you'll know.



Rob.

Cheers :)


X2 I just got a new prop on my boat through them Troy will be able to point you in the right direction.

Ta.

Picture of the prop.. note: extreme edges of each blade have suffered a hit and are kinda bent backward a bit... Worth repairing or replacement?

http://i225.photobucket.com/albums/dd46/Chamelion/IMG188_zpsdeed401d.jpg

Whilst I am here... My skeg is half missing. Still enough there to do the job, but it looks a bit ordinary. Considering fitting a skeg guard rather than getting a new piece welded on.. Are these any good? - http://www.ozpropellers.com.au/skeggard

[Smithy]

Yep might as well get a skeg guard and also get a file or grinder out and touch up all the edges of your prop to get a nice curve again and also sharpen them a bit. Not used one of those guards but worth a try.

[Chamelion]

Cheers :)

What are everyones thoughts on 4 blade props? Had a PM suggesting it has a good alternative to a traditional 3 blade.

[Fed]

Tiny Tack at ebay less than $50.
I'd get the skeg welded unless it's broken off right at the gearbox which I doubt.
3 blades for your boat.

[Fallen angel]

Mate, I would try a 13 inch stainless prop. Pretty much what we ran on a similar set up.

Have you ever tried to re-cup your prop, not hard to do if you have the right tools. You will get a lot more life out of your prop to

[Chamelion]

Cheers for all of the replies so far.. It's sounding pretty clear that I really need a tachometer to see my RPM before going any further.

Would something like this do the job ok? - http://www.ebay.com.au/itm/Hour-Meter-Tach-Tachometer-Boat-Outboard-Mercury-Yamaha-/400230298746?pt=AU_Car_Parts_Accessories&hash=item5d2f95b47a#ht_3567wt_1168

I'd love to get one of these, but too dear at the moment. - http://www.ebay.com.au/itm/Mercury-Mercruiser-Flagship-Tachometer-Gauge-/290772136951?pt=AU_Boat_Parts_Accessories&hash=item43b35eb3f7#ht_500wt_1181

[Fed]

You can't go far wrong at $12.55.

[Chamelion]

This is true.. Have ordered one.

[kind_cir]

This is true.. Have ordered one.

Let me know if it's any good, as I may get one for mine.

[Chamelion]

Will do.. probably be 3 weeks before it gets to my door. I'll test it on the car first.. See how the RPMs on the ebay cheapy match up to the cars on board tacho.

[Chamelion]

Meant to update this.. The tach is junk. Absolutely more or less useless. Turns itself off and on for no reason and often reports seemingly fairly 'out there' readings. I've had it suggesting 6800rpm at WOT one moment and 5800rpm the next, for example.

I've since chunked the prop pretty badly and don't want to risk damaging my gearbox, so I pretty much have to order a prop blindly. I'm pretty keen to try a 13p but will just see what I can find in the 12p-13p range and not worry too much. If 13p ends up as too much when I'm loaded up I'll just have to buy a 12p and have two. One for when I'm solo, one for when I'm carrying a heavier load.

I hardly ever run WOT, usually only small spurts here and there lasting maybe 30 seconds. I'd just like a little more economy at cruise I guess.. Maybe a 4 blade prop is worth a look?

[Chamelion]

Just as a note.. my max RPM is supposed to be 5500. The tach did seem to work for the first half an hour before the whole boat took a bit of a pounding in some chop. It was at that point in time hitting around the 5800 mark, so I don't think going up in pitch is a bad idea. $100~ for a solas 13p prop from the USA is worth a try and I'll keep my eyes out for a better, but not too expensive tacho so I can get a more accurate look at my WOT RPMs.

[Chamelion]

I've ordered a Solas Amita 3 Propeller 3X11 1/8X13R Aluminum - $117.95 delivered from the USA. Nearly double the price here, so I've got nothing to lose. If it turns out unsuitable I'll plop it up for sale and recover exactly what I paid.