Tohatsu 50HP Prop advice needed...

[steelespike]

Re: Tohatsu 50HP Prop advice needed...

You could be fussing about as little as 150 rpm I would go with the 15" Solas. If your at 6000 1" could put you at 5850
on the nose but I think you'll be better off at about 5700.

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

You could be fussing about as little as 150 rpm I would go with the 15" Solas. If your at 6000 1" could put you at 5850 on the nose but I think you'll be better off at about 5700.

I made a mistake in my last paragraph in my last post above... I think with an 11.1 x 14 prop WOT with just me in the boat would prob be 5900 rpm (NOT 5800), 50 rpm above the max recommended! But I'm just guessing!!!

I am assuming that if I had no rev limiter I would be hitting about 6100 rpm with just me in the boat and I am assuming 1" pitch will reduce my rpm by 200 rpm (though some have said it could be 150 rpm).

So as you say an 11 x 15 prop would prob make my WOT 5700 rpm (could even be 5800 rpm with any luck) which is fine, but do you think this is ok when I have 2 other people in the boat with me, as I would guess the WOT to then be reduced by 600 rpm as it is now and thus be 5100 rpm, 50 rpm under the recommended minimum WOT range! Would this be ok? (I would very rarely go WOT with my parents in the boat anyway, though may do with friends I guess!)

 

[pootnic]

Re: Tohatsu 50HP Prop advice needed...

Personally,I like to get as close to the max rpm with a light load as possible.
50 rpm over the max rpm wouldn't bother me but maybe that's just me...

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

In which case you would go for the 11.1 x 14 prop (a 1" increase) rather than the 11 x 15 prop?!

Hmmm, I really am unsure. Will my hole shot be effected a lot with a 2" in pitch increase? Will having an 11 x 15 prop make pulling a rubber ring much hard work? Or even water skiing?! As you can imagine I can EASILY pull a rubber ring with my 11.1 x 13 prop.

 

[steelespike]

Re: Tohatsu 50HP Prop advice needed...

Don't worry about 50 rpm under with a couple more passengers. You can't really prop for every load so sometimes you may be close to or under your lower range, that is completely different than running all the time under your rated rpm.

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

Don't worry about 50 rpm under with a couple more passengers. You can't really prop for every load so sometimes you may be close to or under your lower range, that is completely different than running all the time under your rated rpm.

ok thanks for that!

Sorry to go on, I really want to get this right first time round, as I simply cant afford to get it wrong!

Ok it looks like I will invest in an aluminium Solas 11 x 15 prop in the next couple of weeks, but one last thing, will my hole shot be effected a lot with a 2" pitch increase? Will having an 11 x 15 prop make pulling a rubber ring much harder work? Or even water skiing?! At present, with 2 people in the boat, I can EASILY get onto plane and pull a rubber ring (with 85kg adult on it) with my 11.1 x 13 prop. I would be disappointed if the 11 x 15 prop could not do this, though worse comes to worse I could simply change props for days when I want to use the rubber ring, which is not very often at all.

 

[Sea Rider]

Re: Tohatsu 50HP Prop advice needed...

Assume that engine was factory delivered with a prop, right ? If so, ideal would be testing that prop with you alone and minimun loaded rib, if rpm limiter kicks in, check at which rpm is doing so, go for +1 larger pitch, to drop rpm down, if still kicking in, +1 more and so on till engines runs full wot without rev limiter kicking in. Find annoying to use a light boat and rev limiter kicking in all the time. That would be a state of the art prop/engine optimization, but impossible to do unless you have a full box of props to test.

You are a prime example when stating that factory standard delivered props with engine used on light empty sib/rib & solo driving will produce near max stated factory rpm and in some cases over reving at wot. That's why you must go at least + 1 more pitch to decrease rpm slightly.

That way when going full wot & solo, will know your engine although is high reving it's still under max rpm safe working parameters. When you have dialed the correct size pitch, engine revs will lower accordingly as more weight, passengers is added, still should have a nice response as a rib is much lighter than any other equivalent boat and probably using rib's max HP rated engine.

If you don't trust your current OEM tach, install a portable inductioin tach and double check both wot max readings, you will only need it untill you dial best prop pitch and rev limiter stops kicking in. It's usefull to have at least 2 props, one for standard application, other for different boating activities such as: skiing, pulling inflatable toys, wakeboarding.

Happy Boating

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

Yes my Tohatsu rib/engine was set up at the Tohatsu UK headquarters and came with the stock Tohatsu 11.1 x 13 prop. I trust the stock OEM tachometer. The Tohatsu prop chart shows I can upgrade to an 11.1 x 14 prop and 11 x 15 prop, these are the biggest two recommended props for my engine! In an ideal world I would buy both, test them and return for a refund the prop which was not as suitable, but unfortunately this wont happen and I will have to make an educated guess (with you guys helping! ) on which one to go for, and so far it is looking like the 11 x 15, but I just want to find out a little more re hole shot now, as in my post #26 above!

 

[Sea Rider]

Re: Tohatsu 50HP Prop advice needed...

James,

Why don't you ask Tohatsu dealer at which rpm is the rev limiter kicking in, then deciding if going for a 14 & 15 pitch, don't worry about hole shot, will work fine with any of them due to running a powerfull 50 HP and not a 40 HP that's a more suitable size for a 4.20 Mt rib.

Happy Boating

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

My boat is in Spanish waters now not English, so asking the dealer I bought it from is not really an option. However the Tohatsu manual says the rev limiter kicks in "at approximately 6000 rpm" and my tacho is at 6000rpm when it kicks in!!! Unfortunately I will never know how high my engine will rev to with the current 11.1 x 13 prop because of the rev limiter kicking in, UNLESS I could turn the rev limiter off, which wouldn't be wise! So therefore I would literally have to test the 14" and 15" pitch props and then keep just one, OR just buy the 15" one and hope its the best one, 50/50 chance! lol

I'm glad you think my hole shot will be ok with the 15" prop, can anyone else comment on this? Fortunately I went for the 50 HP outboard for my rib as it was the max recommended HP and also weighs the same as the 40 HP Tohatsu engine, both being 697cc.

 

[jestor68]

Re: Tohatsu 50HP Prop advice needed...

:facepalm:

Just get the 15 pitch for light to moderate loads, as well as higher top speeds with lighter loads.

As you stated (correctly) earlier; you'll end up with two props(like most of us)and stick the 13 back on if needed to pull toys with two/three folks in the boat.

The 15" will be a better all around pitch for general use.

The fact that you are experiencing is that one prop cannot do it all. If you want extreme pulling power, you prop it right up to the rpm limit.

For general running around, you prop it for the middle of the rpm range(which the 15" should accomplish). On those days when you need to pull the tube with three people in the boat, you stick the 13" back on.

The 15 pitch should serve to reduce your WOT rpm by 300-400 rpm, and get you off the rev limiter.

 

[Sea Rider]

Re: Tohatsu 50HP Prop advice needed...

Don't worry, your engine will not be blown in a very short wot spin if you disconnect the rev limiter so to know precisely what's your top rpm as described earlier, that way will know which 14 or 15 pitch to buy. Imagine all the engines that are over reving and owners not knowing anything about it, worst if being newbies.

Seems you haven't had the chance to test that engine/rib combo before going to Spain, right ? So to tell dealer that 13 pitch is over reving and re intalling a 14 that would have been more suitable to start with, and only 15 left for final engine optimization if needed. Still think a 50 is too much for a 420 light rib, as it's near same fast responder model size, 45 diam tubes and less width compared to the oceanic model 420 which has 50/52 diam tubes and much wider, heavier which uses a 40 HP. Anyway, a matter to throttle less while boating with less heavier loads.

Happy Boating

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

Being injection and having an ECU I doubt its a simple case of unplugging the rev limiter!

Indeed your correct, once I had bought my rib the first time it touched water was in the Med! In hindsight I should have immediately contacted the dealer in the UK and said its over revving due to the wrong pitch prop, but I have only just realised this trip out here that I am hitting the rev limiter as its hard to hear! When the rev limiter kicks in the control box emits a constant beep noise which simply sounds like a very high pitched noise when your going along, but it is very hard to hear especially when your doing close to 40 mph with the wind, water and engine noise and holding on for dear life! lol. Also unfortunately the rib is just over a year old now by a matter of days, so its a bit late to go back and complain I think.

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

A 1" pitch change nets 150-200 rpm change. So the 15 should produce 300 to 400 rpm decrease.
The 11 X 15 Solas should work well with a touch more speed and a little slower holesot.

I have just spoken to the UK Solas dealer and they have told me a 1" pitch increase will lower my rpm by 250 - 300 rpm! This is a big difference to what I have read on the net and therefore I would go for a 14" prop and not the 15" prop. I am not sure what to do now, and I was going to order it by latest today as I am going to spain where my boat is a week today!

How sure are you guys that a 1" pitch change nets 150-200 rpm change? Surely Solas should know their stuff 100%?! Thanks.

 

[steelespike]

Re: Tohatsu 50HP Prop advice needed...

Can't really guarantee it.It's a rule of thumb nothing is carved in stone with props.
You might look up nissan/tohatsu prop threads here see if you can find anything.
I would have to give way to the dealer assuming he indeed has experience.
Did you ask him why their props don't follow the norm.

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

I appreciate its a rule of thumb, but from what you and many others on the internet have said the rule of thumb is 150 - 200 rpm change in rpm per 1" pitch change. This is a big difference to what the lady on the phone at the only official UK Solas dealer said to me! She said 250 - 300 rpm change and that I would be better off going for a 14" prop!

I am going to phone the propeller shop in Ireland next (I found them on the net and they sell Solas props and are ?15 cheaper than the Solas dealer in London!) and pick their brain but sods law I bet they say 150 - 200 rpm like most other people!

I think I will also call the UK solas dealer back and ask why she said 250 - 300 rpm. Is it the design of their props? Also I could ask if she is wrong and my engine still over revs with a 14" prop can I change it for a 15" prop.

I think with a 14" prop it will strop me hitting the rev limiter at WOT with just me in the boat and will be fine for when loaded with 2 or 3 people etc so maybe its best to go for a 14" prop, but I guess I really wanted to go with the 15" because I would gain more top end speed and its the same price, fair enough if the 14" was cheaper!

 

[J@mes]

Re: Tohatsu 50HP Prop advice needed...

Right I spoke to Tohatsu UK today and their advice was that they usually see a 200 rpm difference for every 1" pitch difference, and that I would probably be better off going up just 1" to a 14" prop for my general all round use.

I called steel developments back (the English distributor for Solas) and questioned the lady's 250 - 300 rpm estimate for 1" change in pitch and she simply said well we have been working with props for years and this is what we find! Unfortunately after I spoke to her I then looked at their website more closely and read the FAQ section re props, one detailed page was written by this woman I spoke to, so I then gave her more merit BUT on another page on their website I found it says "having the pitch reduced by one inch which will give you the needed 200 RPM... This RPM alteration is presuming a gear reduction of approximately 2:1" So this makes me think she is not actually competent and contradicts herself! However that said the mentioning of the gear reduction ratio confuses me but for reference my gear reduction ratio is 1.85 (13:24) according to my manual.

I also spoke to another UK prop shop who dont sell Solas, but they refurb props so thought I would pick their brain and the guy said to me they find 1" change in pitch changes the rpm by 200 - 250 rpm.

Last company I spoke to was the Irish Solas distributor and to my amazement the guy said 1" pitch will change the rpm by only 100 rpm, YES that is what he said! He said thats the case with big outboards around 250/300 hp. To be honest out of everyone I spoke to I think he was the worse and was simply guessing!

I have searched and searched the net for info and the net seems to say on average either 150 - 200 rpm change or 200 rpm change for every 1" pitch change. Therefore I will assume a 200 rpm change and like Tohatsu UK suggested, I am now swaying towards getting a 14" pitch prop, where as before I was going to buy the 15" one!

steelespike, you have been a great help so far and I appreciate and respect your opinion. From what I have told you, do you still think I am better off with a 15" prop as opposed to a 14" one over my OEM 13"? I think the 14" will be best for when there is 2 or 3 people (or more) in the boat (about 66% of the time) but I am worried that when its just me in the boat the WOT may be JUST over the max WOT rpm, it may be 5900 rpm (50 over) or it may even be 5950 rpm (100 over and just 50 short of the limiter), because the rev limiter cuts in @ 6000 rpm I will never know what it would rev to with my 13" prop, I guess 6100 rpm. The only good thing is at least the 14" prop should stop me hitting the rev limiter!
Now the 15" prop will certainly be spot on with just me in the boat (which is about 33% of the time), WOT will certainly be within the 5150 - 5850 rpm range, but when I have 2 or 3 (or more) people it will certainly not be as good as the 14" prop I think. So like Tohatsu UK suggested, I think I will buy a 14" prop tomorrow, will sleep on it tonight and hopefully have some advice tomorrow morning?!

Sorry to go on everyone and I appreciate your advice. I am on a very tight budget and can only afford to buy one prop once so need to get it right first time round, hence all my questions!!

ps. just thought I'd say in case someone suggests it... none of the companies here are willing for me to buy a 14" prop and exchange it for a 15" if rpm is still too high!

 

[J@mes]

Help!!!

Help!!!

Right!

I finally got round to buying the Solas 11 x 15 propeller to replace the OEM 11.1 x 13 Tohatsu one.

I fitted it today and unfortunately I have to say I am very gutted! =( I am getting bad cavitation, think that's what it's called where the water comes splashing up behind the transom. It never used to do that with the old prop! Also my WOT rpm with just me in the boat has now gone from 6000 rpm on the rev limiter to 5000 rpm!!!! and my max speed is down 2 mph too!

Why on earth have I lost 1000 rpm?! I was expect a reduction of 300 - 400 rpm by going up 2" in pitch (with an increase in top speed!) and also I was not expecting bad cavitation if that's what the splashing I am experiencing is called. I will do some research now but thought I'd ask you guys first! Do I need to raise my motor up one hole to stop this cavitation? TBH I don't want to do this and don't think I will be able to, if I had known this would have happened I would have simply stuck with the OEM prop! Hopefully I can get a refund if this isn't going to be a simple fix!

Lastly I also noticed the exhaust note is slightly different now with the new prop. Thought I'd say in case that's a clue to the problem as it's a through hub exhaust prop!

I appreciate your help, thanks!