Outboard High Thrust prop

[Redfox226]

Hi All
Following on from the interesting thread about a Cat with an outboard, can someone please explain to me which of these:
3 x 7 1/2 x 6
3 x 7 1/2 x 6 1/2
3 x 7 1/2 x 7
three bladed props to fit my Suzuki DF6 has the higher thrust?

Just checkin'
TIA

 

[VicS]

Hi All
Following on from the interesting thread about a Cat with an outboard, can someone please explain to me which of these:
3 x 7 1/2 x 6
3 x 7 1/2 x 6 1/2
3 x 7 1/2 x 7
three bladed props to fit my Suzuki DF6 has the higher thrust?

Just checkin'
TIA

They are all 7½"diameter
6" is the smallest pitch so will be the most suitable for a displacement hull

High thrust props are sometimes a larger diameter and often have large " Mickey Mouse Ear" blades as well as a small pitch.

 

[Redfox226]

Thanks Vic - when the current one needs replacing, I now know which to get.

 

[Tranona]

It will not necessarily give you any higher thrust, just allow the engine to rev more. So if your engine can achieve maximum revs under load with the coarse pitch prop then you will gain nothing by reducing the pitch and may in fact lose because the finer pitch prop will not move you as fast for the same revs.

"High Thrust" outboards have a larger reduction ratio and a larger diameter prop, whereas your engine will likely have a standard reduction and one size diameter and a choice of pitch props to allow for different kinds of boats.

 

[VicS]

It will not necessarily give you any higher thrust, just allow the engine to rev more. So if your engine can achieve maximum revs under load with the coarse pitch prop then you will gain nothing by reducing the pitch and may in fact lose because the finer pitch prop will not move you as fast for the same revs.

"High Thrust" outboards have a larger reduction ratio and a larger diameter prop, whereas your engine will likely have a standard reduction and one size diameter and a choice of pitch props to allow for different kinds of boats.

My 6 hp Yachtwin has a 9¼" x 6½"prop with Mickey Mouse ear blades. The standard engine has a 8½" x 9 " prop. The gear boxes are identical. The difference in overall gear ratio is due solely to the difference in prop pitch.

There are other differences between the engines. in particular the Yachtwin has a 20" shaft as standard and a modified exhaust outlet which allows the engine to be mounted with the prop deeper and to give full thrust when going astern.

 

[Redfox226]

Thank you Gentlemen

The problem arises because of the well in my boat, which requires a short shaft OB. At the time I bought the engine, 'Saildrive' was really only available in long shaft, which was too deep, so looking for an alternative method to get optimum thrust...

 

[VicS]

Thank you Gentlemen

The problem arises because of the well in my boat, which requires a short shaft OB. At the time I bought the engine, 'Saildrive' was really only available in long shaft, which was too deep, so looking for an alternative method to get optimum thrust...

Do you know if the sail drive version has a different gearbox ratio .

If not then fit the same prop . unless its too big, as the sail drive version.

I've not come across any info on a saildrive version so perhaps your dealer can help.

 

[Redfox226]

.....
I've not come across any info on a saildrive version so perhaps your dealer can help.

Vic - Suzuki so far as I know don't have a saildrive version - I bought the Suzuki when I was working based on weight alone, and am now stuck with it! So probably just flying a kite!

 

[coveman]

One point not mentioned is that the high thrust prop should give you better performance and control when in reverse

 

[Tranona]

My 6 hp Yachtwin has a 9¼" x 6½"prop with Mickey Mouse ear blades. The standard engine has a 8½" x 9 " prop. The gear boxes are identical. The difference in overall gear ratio is due solely to the difference in prop pitch.

There is no difference in gear ratio as a result of a larger diameter, flatter pitch prop. The potential shaft speed is exactly the same, but the flatter pitch prop will allow the engine to reach its maximum power and revs more readily.

Worth exploring from the OPs point of view whether a larger diameter flatter pitch is available for his engine. Not familiar with it but it might be limited to the 7 1/2" because of clearance.

 

[Redfox226]

...
Worth exploring from the OPs point of view whether a larger diameter flatter pitch is available for his engine. Not familiar with it but it might be limited to the 7 1/2" because of clearance.

Thanks Tranona - as far as I know these are the only sizes available from Suzuki - I'm also fairly sure that clearance below the cavitation plate may be an issue - a larger diameter would be much more difficult to fit through the well opening....