Prop suggestions for 2011 Tohatsu 15hp?

[smallblock]

I am replacing my prop on my Tohatsu 15 hp 4 stroke and was wondering the benefits of going to a four blade 10 pitch over the stock 3 blade 9 pitch? I am running it on a 14 foot MirroCraft deep V... Any info and manufacturer suggestions would be great appreciated. Thanks for reading...

 

[Sea Rider]

You should have tached that combo with you alone while lightly loaded on flat calm no wind water cond. That 3 blade 9 pitch factory delivered is a medium pitched prop. When you know your max achieved wot revs will know if inside its 5000-6000 rpm wot range for that OB, running towards max wot rpm range would be opt to aim for. Selecting blindly another prop without testing previous standard one is no bueno for engine...

Happy Boating

 

[fishin98]

I and others have found that when you go from a 3blade, to a 4 blade you would normally step down a pitch...in your case from a 9P to a 7P...What exactly are you looking for? Speed or Power(hole shot)(better performance loaded)(fuel economy)

 

[smallblock]

Not to confuse, The combo works great as suggested, light loaded no wind days. I have to replace the prop, so I just want to see what other options are if any. I used the four blade as an example only because it seemed to be the only suggested four blade for that motor on a search. I have pretty decent power out of the hole and good speed when Im alone, but if I add a couple hundred pounds my performance sucks. Im not at all concerned about fuel economy. Would your suggestion be I stick with the stock set up? Thank you...

 

[fishin98]

Looking at the prop selection up in the parts section here on Iboats, looks like you can get into a Solas Amita 4blade 7p for around $70-75. When I switched from a 3 to a 4 blade on my 2000 Merc 90Hp, results were better low end power,and was able to run at a slower plane speed and maintain it. It's your BOATING BUCKS...I suggest a 4 blade 7P.

 

[smallblock]

Thank you... Im hoping to utilize the power a little better so a different prop seems like the way to go. A slower plane speed would be nice as of now I have to to have it mashed to maintain plain. Could someone explain how could avoid going over max rpm at wot? As mentioned above I do not want to blindly risk damage to the motor...The current prop is spun so I wouldn't be able to test it properly without buying a new one exactly the same...Thanks for all the tips and help.

 

[Sea Rider]

By saying that combo works ok doesn't mean it's working around its medium/ max rpm, specially whan it turns out as a pig while adding more weight, you could be lugging OB and not knowing. If you go down one pitch for a 8 while maintaining 3 blade prop, combo will respond much better, should increase + 300-500 rpm your wot range. But only a tach will tell.....

Happy Boating

 

[steelespike]

Right now your basically in the dark though its would seem you need a lower pitch.
Would be excellent if we could get a lightly loaded wot rpm and gps speed.Remind us of the prop size.
Lacking a tach a gps speed would help along with a description of your hole shot a description of results of adding a person.
"Performance sucks" needs more detail. Holeshot numbers,gps speed light load and with 200 added.
Its important that we get the ideal results when dealing with your little 4 stroke.
Your boat may not really be a deep V. If it is then a pronounced V will extend all the way to the transom.

 

[smallblock]

I have no data to support anything I am saying so I guess this conversation is moot. I will replace it with what it came with. Thanks for the help.

 

[steelespike]

Most cell phones you can add a gps app. It would seem that a 8" pitch would help with 200 pounds added.
Some folks would say performance sucks because hole shot is 10 seconds instead of lets say 6 seconds.
Others would be more likely to complain for say 30 seconds to planing speed.
Were not looking for stop watch times.
Are you saying hole shot is slow or poor top speed ,or both?
There are things you can do to help performance without a prop change.
Have you tried different trim settings.Have you tried moving weight around.
There are prop shops that can repair a damaged prop.A good shop could change pitch for more power.
Though on a little prop it may not be cost effective.
Keep in mind that a arbitrary prop change without a little information might result in lugging or over reving the motor,
both bad.
Going to a 8" should help but we don't know if your lack of performance results from a poor setup
or lots of weight.

 

[smallblock]

Thanks for the reply and the info. As of right now we still have about a foot of ice so.... I do have gps but will have to wait. My boat is a pretty light weight 14 foot Mirrorcraft V bottom. The V runs the entire bottom of the boat straightening out maybe a foot before reaching the transom. My hole shot is fine seems fine. When Im alone,(low weight), its seems I reach top speed at about half throttle, adding more throttle just gives me rpm with little to no more actual speed, or so it seems. Often when alone in the boat I cant even reach top speed with out the hull bouncing up and down, trimmed all the way it can go even. I understand putting some weight up front would help with that. My problem is when I take two people out it takes forever to get on plane and my power seems to be about half...Im relatively new to four strokes and has taken me a while to even see a pattern in performance because Im not sure what I should expect...I do have to replace the prop so I was just trying to figure out if maybe a different pitch would be best for this set up.

 

[Sea Rider]

According to my personal experience with Tohatsu OB as we sell them and go boating with, portable OB?s that comes factory delivered with standard medium props performs very well on light to medium light applications. On heavier and larger applications usually must go at least one pitch down to compensate max wot rpm loss which is inevitable. According to Tohatsu once engine has passed its break in period, you should select a prop to suit best your current boating application, very few goes for it...

Go for an 8 pitch, will work much better than a niner powering a heavier combo, included added weight.

Happy Boating

 

[smallblock]

Thank you very much...I really appreciate it.

 

[Sea Rider]

What's the max HP that boat is rated for ? A 15 HP is definitely way underpowered for a 14" footer, you can always maximize a prop to some extend to work much better than with previous factory delivered prop.

Happy Boating

 

[smallblock]

Max HP rating for this MirroCraft is 25 horse. Its confusing to me a little only because they make 2 14 models, one is rated at 15, one at 25. The beam, bow depth and transom height are almost identical. I ran this boat for a decade with a Johnson 9.9 with zero problems. I have one more question, should I stay with a 3 blade prop or go to a four blade assuming I will be going with an 8 pitch to compensate.

 

[Sea Rider]

Do you intend to add an induction tach to your engine, you should do, are inexpensive, can play with pitches all you want and be in the safe side for OB wot range. Don't have experience with 4 blade props, there isn't much OM sizes to choose from, are intended to move heavier boats and loads.

A 3 blade 8 pitch prop will make a difference from a niner. Do you go boating with you alone, friends, it's important to know as the more weight you add the more rpm loss will experment specially at wot.

Happy Boating

 

[smallblock]

Yes probably a good idea to do so. I saw one for 12 bucks on Amazon...I was only curious about 4 blade. I read up on them and it doesn't seem like anything that would apply to me...I fish alone quite a bit but often bring a friend or one or two of the kids...I think I will go with an 8 pitch and see how it goes, but will make sure I use a tach. Do you think I will lose a huge amount of wot rpm? I reach wot rpm at about half throttle when Im alone, if that makes any difference...

 

[Sea Rider]

Check that that induction tach has programmable firing sequence or won?t read accurate, Always use Hardline, Hour/tachs. Will like those once installed on tiller arm near grip. Usually maximize all my OB props to reach max wot range with me alone, add passengers or load to a point wot revs will stay in middle range for OB to run stress free at full grip.

Test niner pitch prop with tach, record the max wot rpm, install new 8 pitch, definitely will see + 300-500 rpm wot increase. Post both props rpm results. Wot range for that OB is 5000-6000 rpm.

Without a tach won't know if you reached wot rpm at mid throttle, probably are planing at mid throttle which is a different story.

Happy Boating

 

[steelespike]

Max HP rating for this MirroCraft is 25 horse. Its confusing to me a little only because they make 2 14 models, one is rated at 15, one at 25. The beam, bow depth and transom height are almost identical. I ran this boat for a decade with a Johnson 9.9 with zero problems. I have one more question, should I stay with a 3 blade prop or go to a four blade assuming I will be going with an 8 pitch to compensate.

I think the differences are fairly significant the 4604 is 4' 10" with a 27" bow depth and a 15" transom 175 lbs 835 capacity,
The 4650 has a 5' 4" beam, 30" bow depth 15 or 20" transom 195 lbs and 950 capacity.
I think the 30" bow depth may increase the overall depth slightly.

 

[smallblock]

Thanks for walking me through this SeaRider. Good point about planing at half throttle, it just doesn't seem to rev any higher after that, or go any faster. We still have ice everywhere so it will be a while before I get out and test anything but will post when I do get results. Thanks again.

Steelspike, good point, they just seem to be very close, although I do wish I had a larger transom depth. Slowing suddenly is a bit scary sometimes but have never had any water come over the transom. The weight of this motor keeps it pretty low in the water..