Tohatsu 9.8 speed

[Sea Rider]

Don't hurry, need to test combo on flat calm, no wind water cond. Testing on choppy cond could be a PITA checking OB/transom height properly. Test when cond are favorable. What's current prop pitch number stamped on prop body ?

Happy Boating

 

[Tohat9.8]

All prop says is F7. Agree no rush.it was spring walleye run this last weekend. Mayhem. Problem is I have no lakes nearby that allow gas motors. Closest is rivers. In a few weekends I can take to a lake early in morning. Maybe I can call Tohatsu. I think it is original prop. I know diameter is 9".

 

[Sea Rider]

Is tach installed right, 3300 wot revs are extremely low, check probably was set wrongly to 1 pulse per revolution when needs to be set at 2 pulses.

If set OK and OB achieved 3300 wot revs with a 7 pitch prop don't think that with a 5 pitch which is the smallest available pitch will ever make that OB to run near min 5 K wot revs. Probably boat is to much for such underpowered OB, anyway if after dialing sweet OB/transom height combo doesn't want to plane, content with a much better fast displacement speed that before.

Happy Boating

 

[pvanv]

Odds are transom height and trim need adjustment -- especially height. Low = slow. The ESG limits at about 6250, so if tach is showing 3300 and set wrong by 1/2, could be hitting rev limiter, but I doubt that.

 

[Sea Rider]

According to my experience with 3 Tohatsu OB's, all needed badly a prop maximization in order for all of them to run at least middle to max wot rpm range with a constant medium load., OB's needed 1-2 less pitch from factory delivered powering light Sib/Rib inflatable boats. Let's see what OP finds out..

Happy Boating

 

[Tohat9.8]

The pitch on prop is a stock 7. I called Tohatsu. Iboats has a 6.5 pitch. Would prefer 6 pitch. Also the tach was set right I think because it was reading right about 900 in forward gear at idle, matching Tohat spec. I would like to throw that OB onto a rowboat type vessel, lighter than mine. I may have opportunity in early May. However that will make AV plate really below keel. Sea rider what is OP?

 

[Tohat9.8]

Ok I bought a 4 blade 5 pitch propr. Needed one anyway bc I discovered one of my blades is slightly bent! It must have happened in Wisconsin this weekend when without much warning I hit a pothole type gravel repair area on highway. But to be honest the OB went as fast as always, which is slow. Will try new prop, mess a little with OB pitch, maybe try to raise motor as much as I can on next test run.

 

[pvanv]

The Tohatsu/Solas 5-pitch high-thrust prop is intended for heavy loads such as sailboats (I use one on my 9.8 pushing a 7,000-pound, 28-foot sailboat), and get 5 or 6 K speed, depending on wind and waves. Those props are also designed with a very large diameter hub, to give a lot better performance in reverse. There are actually 2 versions of the 4-blade HT prop. The 5, which works for really heavy loads, and a 7 pitch, which we use on lighter sailboats. In some cases, these props work well on some RIB applications, as they really "shovel" a lot of water at slow speeds, which helps hole shot.

 

[Tohat9.8]

Paul. Figured I would try. If no good will go to a 3 blade 6 pitch.

 

[Tohat9.8]

I found a tohat 8.3 x 6 pitch. Gonna return the 4 blade high thrust I think.

 

[pvanv]

I found a tohat 8.3 x 6 pitch. Gonna return the 4 blade high thrust I think.

Try it first.

 

[Sea Rider]

Try them all and stay with the one that achives OB to run at least middle to max wot rpm range as currently loaded. BTW, OP is : Original Poster.

Happy Boating

 

[Tohat9.8]

Will do. I will be able to get to a lake this Saturday, early so I can test on calm waters. Hopefully one of the props helps.
OP

 

[Sea Rider]

OK, just for the record, post max wot rpm achieved with each prop tested as usually loaded, specify pitch and number of blades. Will be interesting to see how pitch, number of blades affects wot rpm.

Happy Boating

 

[Tohat9.8]

Ok guys. Last post. Good news. I put the 6 pitch prop on. Tested last nite. 2 people in boat. Regular gear load. At WOT I achieved 5400 rpm. Had 3300 rpm previous. Achieved top speed of 14 mph. Into a 12 mph wind. Previous best was 7 mph going with river current Water rode perfectly under plate as searider described. I am now thinking I perhaps did notice bent prop blade to begin with?

 

[Tohat9.8]

Correction. Did NOT notice bent blade. Thanks for help and input!

 

[Sea Rider]

Correction. Did NOT notice bent blade. Thanks for help and input!

Are you happy with final performance ? if would like OB to rev as loaded towards max wot 6 K range take prop to a prop shop and have it repitched to 5.5. At 5.5 K OB is right at middle wot range. Which is good, but could be bettered.

Happy Boating

 

[Tohat9.8]

Will consider that Sea Rider. Thanks again!

 

[Sea Rider]

Will consider that Sea Rider. Thanks again!

Just for the record, did water flow at speed dialed right under upper deflector plate or had to lower or raise OB a tad for that to happen ? Great performance improvement due to OB height along a maximized prop running up/down river.

Happy Boating

 

[boater1234]

Just wanted to chime in on the holes left by the fin. If you want you can fill them with a putty epoxy,sand the holes down level with the rest of the anti ventilation plate and prime and paint . I've done it to tons of outboards and it's easy as cake and takes very little time. You can also just leave it be but if you plan on going up in size and want to sell it down the road some people may get turned off by the holes. Just figured I throw that at you. All you do is put masking tape under each hole so it holds the putty and your good to go,of course you need to do all the prep work before you fill the holes and before you paint. That motor is a great runner. I love tohatsu, I can't wait for the new 15/20hp efi to come out in the fall so tohatsu is saying. Good luck with your outboard.