Tohatsu 9.8 prop?

[Chopperbill]

It's on a 12' inflatable. Planes running solo and runs 16 mph. Very happy with that because I'm at 5000' and I know I could use more HP. Add a130# passenger and it won't plan and will only do 8 mph. Called a dealer and he said a prop change would do it. All that is available is a 8.5 x 7p. (He had a 5p but did not recommend it) Mine stock is 7.5 pitch. Hard for me that this will help much. Any ideas?

 

[steelespike]

With the little motors a small pitch change can be effective. Thats why they have those type props.
There are only 3 props available here where a 50 hp might have a dozen or more.
Be sure the boat is fully inflated.Try different trim settings.We had a very similar thread recently.
You might try a search.

 

[Chopperbill]

Has anyone out there gone from a 7.5 to 7? If how difference was there?

 

[steelespike]

Do a search for" tohatsu in props"This should give you an idea what your could get.
Results aren't necessarily lineal.I think he went from a 8" to a 7" Went from 8" with 2 aboard not planing to 7"got 5900
rpm and 14 mph.was able to cruise at 11.
By the way looked up today specs on a 9.8 are a 8" prop standard.

 

[Chopperbill]

Now I'm confused!! My motor is a 2011 and supposably had only 20 hours. It has a 7.5. Looked up prop chart in manual and it says 10" is standard and an 8" isn't even listed. Jezz, I don't know where to even start from. Prop maybe have to small a pitch? On edit: can't even find a 10" listed any where. WTF! Wish the built these damn things in the USA.

 

[steelespike]

First you need to know that all boat motors need to be able to reach their designed wot (wide open throttle) rpm range.
They will lug if they operate at too low a wot rpm may cause premature motor problems.
Its ok to occasionally lug a motor if its not a usual thing. If you usually have a passenger you need to prop for that.
If propped for a passenger you need to be aware that the motor may over rev with you alone.Just throttle back a little once on plane.
Maybe I should explain Pitch.
Higher numbers say 10" are harder for the motor to turn but will produce more speed if the motor can spin them up.
But higher pitch will struggle more as you add weight like overdrive in your car going up a steep hill.
Lower numbers are easier to turn and respond better to added load. But like the lower gears in your car won't have as fast wot speed.
In your case the boat won't plane with 2 aboard with a 7.5 prop near as I can tell your only choice is a 7" prop.
Your inflatable doesn't do well with added weight and your at 5000 feet so you need less pitch.
I did a brief search for Tohatsu props I found many some at iboats and on the net. and on ebay.Including the hard to find 10"
I can't guarantee a 7" will plane your boat but we know your 7.5 won't.
I don't think props smaller than 7" will make enough speed to plane they are propably intended for kicker motors so they can reach designed rpm
at wot on much larger boats.
By the way Tohatsu supplies some motors to Nissan and Mercury.

 

[Chopperbill]

Thanks for the info. Don't know why my manual says a 10 ". Think it's screwed up. Then I don't know why it came with a 7.5. Again something is screwed up. A 7 might do it but after awhile I get kind of pissy throwing money and time at something that doesn't work. After buying a tach, prop, fuel to drive to the lake and state park fees I got another $150 invested. About convinced myself into putting that money in a new 20hp fuel injected Suzuki.

 

[steelespike]

The on line description indicates a 10"
If motor was sold where 5000 ft boating is likely it would probably have something other than a 10"
On a ridged hull 12 or 14' it would probably do ok with a 10 at sea level.
Suzuki is an ok motor but your already complaining about trying to find parts/props etc.
Suzuki isn't exactly bragging about its vast dealer network.
You should check out the Evinrude 25 I can guarantee you won't have to search for parts and service.

 

[Chopperbill]

Can't really say I'm complaining about parts available, don't exactly live in boat country. Not even a boat dealer in this town of 100,000. Checked on 5 Evenrude dealers here in CO, not one lists any motors. Defender wants $3700 for a Evenrude 25. All other 20hp brands are $3400 and up except Tohatsu is $2700 for a carbed engine. Colo dealer Suzuki dealer lists motors but they want $3700 for a 20 hp. Porta boat Suzuki FI 20hp is $2625 and less a $300 rebate is $2325 delivered to my door. Suzuki only weighs 97# much less than the others. Those are my reasons for looking at Suzuki.

 

[steelespike]

Well you sure did your homework and no doubt the Suzy is a portable 20 hp at the right price.
There is a reason its under 100 lbs. It's only 20 cu in.The Evinrude 25 is 35 cu in.
​ Couldn't find a Suzuki test but the Evinrude will push a 16' 9" 280 lb Starcraft with 2 men battery fuel and gear to 31 mph.
It will get over 16 mpg at a leisurely 4500 rpm @ over 21 mph. It does out weigh the Suzy by 50 lbs but there is a reason.

 

[Chopperbill]

Apples to apples the suzuki 25 is 32.8 ci. The 20 is less than 2 ci than comparable comparisons. Weight is a very important factor to me. These old bone would suffer over 100#, a main reason I am not looking at the max 30hp motors. You make a good Evenrude salesman, now if you can knock off 50# and a thousand bucks you'll make a sale. LOL. Thanks for all the info. New guys like me can use your help.

 

[Sea Rider]

All these tech points are against you ;

-Air inflatable deck.
-Badly engine/transom height matched.
-Underpowered engine when min is 20 HP and you only have a 9.8 HP
- At 5K Ft of elevation your engine has passed from 9.8 to a 7.5 HP.
-Standard prop with too much pitch for 5 K of elevation.

Better go straight for any 20/25 HP engine to match that 365 sib.

Happy Boating

 

[steelespike]

Apples to apples the suzuki 25 is 32.8 ci. The 20 is less than 2 ci than comparable comparisons. Weight is a very important factor to me. These old bone would suffer over 100#, a main reason I am not looking at the max 30hp motors. You make a good Evenrude salesman, now if you can knock off 50# and a thousand bucks you'll make a sale. LOL. Thanks for all the info. New guys like me can use your help.

I have to go with you on the weight at 71 my shoulders and back can't take it either.Also if I have to bend over to look under something I have to lean to the right or I'll trigger my vertigo. lol

 

[Chopperbill]

Yeah, I biggest fear is dropping something and having to pick it up.

 

[Sea Rider]

Why don't you try as last option a set of trim tabs at back lower transom, probably will help to plane out with 2....

Happy Boating

 

[Chopperbill]

Too much screwing around to make the Tohatsu work and will still have a dead horse. Put it on Craig's list. New Suzuki FI 20hp will be ordered Monday. FI will be a big plus at this altitude. Will kick some serous ass at sea level this winter in AZ. You guys have been terrific.