outboard prop

[sailingjeff]

Hi
Does anyone have any experience of props on a 2stroke 8hp ob ?
My prop is 8.7 x 5 and fat out I can only get 4.5kts. I am thinking a bigger pitch, maybe 6 will give better performance. Would be grateful for any thoughts received and boat is a first 211.

Thanks

Is it ever going to warm up !²

 

[VicS]

5" pitch is very fine but it depends on the gear ratio. You dont say what engine!

Both my Evinrude 6 hp Yachtwin and the 8 hp version have 9¼" x 6½" props The 6hp engine runs at 5000rpm max, the 8 hp at 5500 rpm. Gear ratio is 13:29 for both.

Standard 6 and 8 hp engines have 8½" x 9" props.

The prop fitted to the Yachtwin is also a high thrust prop with big "Mickey Mouse ear" blades.

What props are available?


Is it a rubber bushed hub ? if so is it slipping ?

 

[sailingjeff]

Hi,

The engine is a Tohatsu but I am afraid I do not know the ratio. My manual says about the same for max revs. However, I think you have confirmed what I thought, that the pitch is too fine. I can get up to about 8.5 pitch I think so I will have a go at increasing it.It might improve the fuel ecomomy too.

 

[Steve C Cronin]

Is it this one? If so, ratio is 2.08:1
http://www.outboard-engine.com/enginespecs.php?recordID=153

 

[VicS]

Is it this one? If so, ratio is 2.08:1

Apart from being expressed the other way round that's not vastly different to the ratio for the Evinrudes. The prop would be turning a little faster for the same engine revs so a slightly finer pitch than the Evinrude would be in order perhaps . Id suggest around 6" as the finest and 8" the coarsest to try.

 

[TSB240]

I have a tohatsu 8 and 9.8 Hp 2 stroke obs and have used both on a similar trailer sailer.

I fitted 4 blade high thrust saildrive props and the difference is amazing. I can happily motor into a big chop with no problems. Loads of bottom end grunt and instant stopping power at low revs. The prop you have is as much use as an egg whisk on your baby bene.

Tohatsu part no is 3b2b645120 8.7" dia 7 pitch 4 blade

http://www.tohatsu.com/accessories/prop.html#Tohatsu Outboard Propeller Chart

Steve


Solas might have a lower priced alternative.