A question of thrust

[kolyo]

I wonder which of the two will be more thrustworthy ?

a) Yamaha T9.9 High Thrust (212 cc block)

or

b) Suzuki DF20 (327 cc block) with a high thrust aftermarket propeller

 

[BruceK]

Is this a trick question?

The Yamaha High Thrust gives 60% more thrust than it's own equivalency so very loosely the performance a 16 hp would.

The DF20 is 20hp off the bat,

I would be floored if the 212cc block had the same torque as the 327cc block

So as long as the aftermarket high thrust prop was efficient on the DF20 allowing it to lay out all it's hp power without bogging down (to negate a higher gearing) it would be better

 

[kolyo]

Not a tricky question at all. I'm looking for the best power/thrust/weight ratio option for a trolling kicker for my fairly heavy, high windage 25 ft. flybridge boat.

Thanks for your input!

 

[ontheplane]

Again, the 20 would seem the obvious highest thrust - however that assumes it is geared and propped properly as neither will achieve planing speed. However the Yam will be lighter I'm guessing.

Are you coastal or inland? The 9.9 will be plenty inland, but may struggle depending on wind age coastal, but would give you steering and so forth.

 

[kolyo]

Coastal, and the weight difference is negligible for a 3.5+ ton boat. The drawback of the Suzuki is no 25-inch shaft option.

 

[ontheplane]

I was more thinking of lifting it off and on - may or not be an issue.

Yamaha do a 25HP High Thrust - I don't know if you are looking at new - but if so, I suspect that this will do a very good job for you - I guess it's also a question of cost but if that's not such a consideration then the 25 does come in a 25" shaft and would have a serious amount of kick with a 432cc engine

Uk site here - T 25hp - marine-engines - Yamaha Motor

more info on the American site here - Yamaha Outboards

Looking - the tiller is optional on this engine and it's pretty heavy (91 kgs) but I suspect if it would all work for you that would be a great motor for the job.

 

[kolyo]

I was considering the T25 but the weight put me off. Also I intend to use the Garmin Reactor 40 autopilot which is rated for outboards up to 20 hp max.

 

[ontheplane]

Yep, as with all these things - a compromise.....

How does that Garmin work and why is the limit a 20?

 

[ontheplane]

Cant help but think if the transom mount is up to it, and the weight is tolerable and the price isn't a killer, that T25 looks a way better bet for you

 

[kolyo]

Garmin Reactor™ 40 Kicker Autopilot | Small Gas Boats

Lots of claims in the fishing forums it's the best (if not the only) reliable AP option for a trolling outboard.

High Thrust Outboard Motor Bracket | Adventure Marine MFG

 

[ontheplane]

Yeh, don’t think that outboard bracket would take the 20 never mind 25 high thrust.

Also, with it sticking back so far, if there was a lot of fore/aft pitch, wouldn’t the outboard come out of the water?

 

[ontheplane]

Garmin kicker - £2500 just to hold an outboard steady - bloodyhell!

I’d use a bit of rope!

 

[C08]

The Yamaha 9.9 (I think) has a much higher (numerically() gear ratio than a standard 20hp so will probably swing a bigger prop than the 20hp. Aftermarket hi thrust 4 blade props are not as good as cracked up to be in my experience. I would go for the 9.9.

 

[C08]

I was considering the T25 but the weight put me off. Also I intend to use the Garmin Reactor 40 autopilot which is rated for outboards up to 20 hp max.

I have just fitted a 25hp Yamaha long shaft hi thrust model and it is very large and about 100kg. I have not had the opportunity to use it properly as running in and then lockdown.

 

[ontheplane]

Be interested to hear your views on it - I bet that has similar thrust to a normal 40hp - way less speed of course, but a lot of grunt.

 

[kolyo]

Yeh, don’t think that outboard bracket would take the 20 never mind 25 high thrust.

Also, with it sticking back so far, if there was a lot of fore/aft pitch, wouldn’t the outboard come out of the water?

I'd never use a trolling outboard in any sizeable for/aft pitch conditions. When this happens I just fire up the main I/O.

 

[kolyo]

The Yamaha 9.9 (I think) has a much higher (numerically() gear ratio than a standard 20hp so will probably swing a bigger prop than the 20hp. Aftermarket hi thrust 4 blade props are not as good as cracked up to be in my experience. I would go for the 9.9.

Thanks, I much prefer advice stemming from experience rather than hearsay.

I also have the sneaky feeling that a "thoroughbred" high thrust, even as low as 9.9 hp, would have more low-end muscle than a twice as high hp "normal" outboard, even if fitted with an aftermarket high thrust prop. The goal is to find the right motor that will push my boat at hull speed (approx. 6 knots) in calm to 1-2 ft seas.

 

[C08]

Thanks, I much prefer advice stemming from experience rather than hearsay.

I also have the sneaky feeling that a "thoroughbred" high thrust, even as low as 9.9 hp, would have more low-end muscle than a twice as high hp "normal" outboard, even if fitted with an aftermarket high thrust prop. The goal is to find the right motor that will push my boat at hull speed (approx. 6 knots) in calm to 1-2 ft seas.

I have a 8M Catalac catamaran and lots of these boats have hi thrust 9.8 & 9.9 engines. The gear reduction ratio of these is about 2.92:1 well suited to a displacement boat. Several people I know have had these engines and also larger engines and anectdotaly many of these people think that the 9.9 high thrust has similar performance to a 20/25hp which with its 2.08 (say) gear ratio swings a much smaller prop. My friend who had a 9M catalac with a 9.9 had very similar performance from the engine to my 20Hp Tohatsu (9.25" prop), with better fuel usage.

 

[kolyo]

I have a 8M Catalac catamaran and lots of these boats have hi thrust 9.8 & 9.9 engines. The gear reduction ratio of these is about 2.92:1 well suited to a displacement boat. Several people I know have had these engines and also larger engines and anectdotaly many of these people think that the 9.9 high thrust has similar performance to a 20/25hp which with its 2.08 (say) gear ratio swings a much smaller prop. My friend who had a 9M catalac with a 9.9 had very similar performance from the engine to my 20Hp Tohatsu (9.25" prop), with better fuel usage.

The lower unit of Yam T9.9 high thrust is massive, nearly twice the size of the normal F9.9. Curious why did you chose to replace your Tohatsu 20hp with a Yamaha T25 (which has a 2.08:1 reduction ratio) rather than a T9.9 with it's 2.92:1 ratio? Your 8M Catalac looks to me the same weight as my Bayliner 2556 Command Bridge.

 

[C08]

The lower unit of Yam T9.9 high thrust is massive, nearly twice the size of the normal F9.9. Curious why did you chose to replace your Tohatsu 20hp with a Yamaha T25 (which has a 2.08:1 reduction ratio) rather than a T9.9 with it's 2.92:1 ratio? Your 8M Catalac looks to me the same weight as my Bayliner 2556 Command Bridge.

Sorry I bought a high thrust FT25 yamaha which has a 2.42 gear ratio and a 13" prop, compared to my Tohatsu with a 9" prop and a lower gear ratio but still a nice engine.