Tohatsu 50HP Prop advice needed...

[J@mes]

Hi there,

I have a Tohatsu 50hp TLDI outboard on my 4.2m rib and with the stock prop, 11.1 x 13, according to GPS I can hit 39mph on my own in the boat. I have looked at the Tohatsu properller chart and it says the maximum I can fit is a 11 x 15 pitch prop. I am courious as to how much extra top speed this would give me? I appreciate it is very hard to say with all the variables etc, but what would your guestimate be? 2mph, 4mph increase or more? I have never changed/played with props before so have no idea and would like a rough guestimate before spending money to find out I have only gained 1mph! lol.

Thanks for your help,

James

[martini]

You'll lose speed if the motor hasn't got the power to spin a coarse pitch prop. If you want to try and improve performance, the first thing you need to do is hook up a tachometer, either installed on the dash or a test meter temporarily hooked up to the ignition system.

Comparing results with the max rpm rating of your motor might give you an indication as to wether another prop will help

[J@mes]

I already have a tachometer installed!
I appreciate what you say, but if the engine was not powerful enough to spin an 11 x 15 prop then surely Tohatsu wouldnt list it for my engine?!

Thanks.

[Kiss my bass]

Originally Posted by J@mes

I already have a tachometer installed!
I appreciate what you say, but if the engine was not powerful enough to spin an 11 x 15 prop then surely Tohatsu wouldnt list it for my engine?!

Thanks.

It's powerfull enough to spin it, right up to the point you put the engine on a boat, tohatsu won't know what size weight every boat is, the size they list is what the engine will take, but what works on one boat may not work on yours.

The answer already given is good advice, you need to look at the rev figures you are getting now as to what to do next

[J@mes]

Well I think WOT is 6k rpm from memory with just me in the boat = 39mph.

Also from memory with my dad in the boat (+ 85kg) the top speed is 35mph and I think the WOT is slightly less, maybe 5800 rpm.

What advice can you give from this?

Also just noticed on the Tohatsu chart is also states the stock prop 11.1 x 13 is for a boat with a moderate weight load (500-1500 lb.) but it says for a light weight load (100-500 lb.) then a 11.1 x 14 or 11 x 15 prop is recommended. Well according to this I only ever have a light weight load!! I appreciate your comments re every boat is different, but with their loading advice in mind and the fact my rib is not a heavy rib (116kg bare boat + 98kg engine + weight of battery/consol/steering/fuel etc I would conservatively guess 300kg max all in) I would have therefore thought an 11 x 15 prop would be ideal for my rib?!

Cheers,
James

[Kiss my bass]

Provided its the same as my 50 tldi then the max revs should be 5850, if it hits 6k then the auto cut out should kick in, so on the basis of the revs given, I would say your under propped when alone, but about right 2up, if you go up a size then performance will probably suffer as it will top out before it reaches full revs.

[matt h]

Just buy the prop n try it, its the best way.

[J@mes]

Originally Posted by Kiss my bass

Provided its the same as my 50 tldi then the max revs should be 5850, if it hits 6k then the auto cut out should kick in, so on the basis of the revs given, I would say your under propped when alone, but about right 2up, if you go up a size then performance will probably suffer as it will top out before it reaches full revs.

My manual says WOT should be 5150 - 5850 rpm and from memory the rev limiter/auto cut out kicks in at 6150 rpm

Why do you think If I go up a size (I assume you mean to a 15" pitch prop?) performance will probably suffer? Surely with just me in the boat at WOT it will come down from 6000 to about 5800 rpm and with 2up to about 5600, either way it's inside the WOT 5150 - 5850 rpm range stated by Tohatsu!

Originally Posted by matt h

Just buy the prop n try it, its the best way.

If only money grew on trees!! Plus if it made my performance worse it would get removed from my outboard and would have been a waste of money and time, hence me asking here first!

[Locozodiac]

If already achieving 6K at wot with you alone, personally would stay there, it's normal that with more weight rpm will be slightly decreased. The top speed difference between standard delivered prop and next adyacent pitch is minimal, not cost effective.

Is 39 MPH not enough for you ? More top speed, lessens better hole shot and viceverse. Placing a 15" prop will decrease rpm by 200-300 rpm. Probably will benefit achieving better hole shot with slight top speed than with 13"

Happy Boating

[spartacus]

If you were local - you could borrow my 15 pitch propeller, on the understanding if you damage it you replace it with a nice shiny stainless steel one!

Any Ribnet members near you - you could swap propellers with?

[clydeoutboards]

Originally Posted by J@mes

Well I think WOT is 6k rpm from memory with just me in the boat = 39mph.

Also from memory with my dad in the boat (+ 85kg) the top speed is 35mph and I think the WOT is slightly less, maybe 5800 rpm.

James

Hi

2 v quick points

1: you are right to ask advice as many people throw money a things like props expecting a huge difference and unless its a few sizes the change will be minimal and as stated before bad bang for buck. There are also different types of props and other things you can do to help performance that would be cheaper in most circumstances.

2: you imply that these figures are a good guess and not 100% and hence the first thing I would do is check these. If i have miss read then v sorry.

Dave

[J@mes]

Originally Posted by Locozodiac

If already achieving 6K at wot with you alone, personally would stay there, it's normal that with more weight rpm will be slightly decreased. The top speed difference between standard delivered prop and next adyacent pitch is minimal, not cost effective.

Is 39 MPH not enough for you ? More top speed, lessens better hole shot and viceverse. Placing a 15" prop will decrease rpm by 200-300 rpm. Probably will benefit achieving better hole shot with slight top speed than with 13"

Happy Boating

My hole shot is very good at the moment and I don't mind sacrificing a bit of it for a little bit more top speed. Is 39 mph enough, well you know how it is, boys and there toys lol, yes I would like a little more if possible by simply changing the prop, but don't want to spend a lot of money on it as tbh I don't think its really worth the bang for buck!

Originally Posted by spartacus

If you were local - you could borrow my 15 pitch propeller, on the understanding if you damage it you replace it with a nice shiny stainless steel one!

Any Ribnet members near you - you could swap propellers with?

I would love to be able to try someone else's prop, but my problem is my boat is in Spain, though I am next over in 3 weeks time. Don't want to lend me your prop do you?! lol

Originally Posted by clydeoutboards

Hi

2 v quick points

1: you are right to ask advice as many people throw money a things like props expecting a huge difference and unless its a few sizes the change will be minimal and as stated before bad bang for buck. There are also different types of props and other things you can do to help performance that would be cheaper in most circumstances.

2: you imply that these figures are a good guess and not 100% and hence the first thing I would do is check these. If i have miss read then v sorry.

Dave

What other cheaper things could I do to help my top speed? I don't carry unnecessary weight in the boat so its not like I can make it lighter.

You have read correctly, I cannot say 100% WOT is 6000 rpm with just me in the boat, I need to double check when I next get a chance!

[clydeoutboards]

Well we have customers who have been on diets to waxing the hull, changing the ballence of the boat etc. Its not for me but hay if thats your thing then go for it.

You have a great set up so first I would check the numbers and take it from there.

Dave

[Locozodiac]

Some issues not clear :

You are curently running a 13" factory delivered prop, right ? Is rev limiter kicking in at 6150 with same prop ? If so, will need to go 2 pitches up to 15" so engines lowers it's max rpm achieved and works safely around 5500 rpm, which is the middle numbers between min 5150-max 5850 stated factory parameters.

Personally don't like to go boating alone with an engine with rev limiter kicking in constantly when giving juice and playing near max throttle, if placing a 14" pitch prop will be around 5850 rpm which are much better numbers than over reving.

As this is not exact rocket science playing with prop pitches under trial and error is a must do. Try to find a good Spanish Samaritan that can lend you a 14" to test at wot.

Happy Boating

[J@mes]

Originally Posted by clydeoutboards

Well we have customers who have been on diets to waxing the hull, changing the ballence of the boat etc. Its not for me but hay if thats your thing then go for it.

You have a great set up so first I would check the numbers and take it from there.

Dave

Well I will definitely check when next out there, but I'm pretty sure its close to bang on 6000rpm WOT with just me in the boat and 5800rpm with me and my dad. I don't think I'm more than 100 rpm out tbh. But either way I think it would be safe putting a 15" prop on because it will lower the WOT rpm to within the correct rpm range, 5150 - 5850, I really don't think (hope lol) that my memory of it is that far out!

Originally Posted by Locozodiac

Some issues not clear :

You are curently running a 13" factory delivered prop, right ? Is rev limiter kicking in at 6150 with same prop ? If so, will need to go 2 pitches up to 15" so engines lowers it's max rpm achieved and works safely around 5500 rpm, which is the middle numbers between min 5150-max 5850 stated factory parameters.

Personally don't like to go boating alone with an engine with rev limiter kicking in constantly when giving juice and playing near max throttle, if placing a 14" pitch prop will be around 5850 rpm which are much better numbers than over reving.

As this is not exact rocket science playing with prop pitches under trial and error is a must do. Try to find a good Spanish Samaritan that can lend you a 14" to test at wot.

Happy Boating

Yes factory 11.1 x 13 prop is currently on. I have never heard the rev limiter, I assume you would hear it like in a car?! Also the ECU has not logged any over revving fault codes (I checked for fault codes when I last put my boat away), though that's assuming it would log a code for over revving?!

Yeah if I don't bite the bullet and buy a 15" prop before I go out there then I will definately try and find someone with a 15" prop to try, but tbh I think I will struggle to find someone!

Lastly, If I was to buy a new 11 x 15 prop, do you think I should get an OEM Tohatsu one, or something else like a Solas one? From the few pictures I have seen online, dare I say they look very similar, maybe even Solas produces the OEM Tohatsu props?! Any ideas? Also can you recommend a cheap place online to buy a new prop? Thanks.

[J@mes]

Whoops double post, please delete.

[Locozodiac]

Solas costs bit less than original, as long the size and pitch are correct not an issue. As an example boating solo with a light rib and factory delivered prop my horse achieves full 5800 rpm, that's max 5800 factory stated.

Preffer to be on top max rpm, when boating with 1- 2 more mates max rpm will decrease accordingly, but will remain inside safe working readings at wot. So a prop pitch that will give near or max rpm at wot with will be good to consider.

If not mistaken, TLDI engines don't show a code when rev limiter kicks in, just faulty engine codes.

Happy Boating

[J@mes]

Ok thanks for that. When the rev limiter kicks in, does the engine make a noise like in car? I certainly haven't heard any similar or unusual noises, actually come to think about it I have, I think from memory on the very odd occasion at WOT I have heard a very high pitched noise, but I was pretty sure the noise was coming from the front of the boat!!! As stupid as it sounds it never worried me as it wasn't a bad sounding noise, but I assumed it was the pressure release valve from one of the air chambers at the front of the boat making the noise due to the fact the boat was going fast and skimming the water, maybe putting extra pressure on the tubes? I don't know, think I have just made myself look stupid?!! lol

[ian parkes]

James i have a tohatsu 50 on a small rib and get almost identical performance to you with the standard prop . I tried a stainless prop just one pitch more and it did give a bit more top end with no load in the boat . However add a bit of load or pull a ringo or skier and its was slower dropped too many revs and used more fuel cruising .

I have gone back to the standard prop

[J@mes]

Originally Posted by ian parkes

James i have a tohatsu 50 on a small rib and get almost identical performance to you with the standard prop . I tried a stainless prop just one pitch more and it did give a bit more top end with no load in the boat . However add a bit of load or pull a ringo or skier and its was slower dropped too many revs and used more fuel cruising .

I have gone back to the standard prop

Hi Ian, thanks for the input, that's very interesting to hear!

Sounds like we have a similar set up going by your username info, your rib is 4.3m and mine is 4.2m.

Out of interest how much more top end did you get with no load using a stainless 14 prop? 2, 3 mph extra?

If I was to get an 11 x 15 (alloy) prop I was planning to simply pop the standard 11.1 x 13 prop back on for days when using my rib for tubing/skiing! That was assuming I needed to, which seems the case from your experience! Though even still I hardly use the ring or ski nowadays, and it wont take long to change the prop if needs be I guess.

Hmm you have made me think now, I think maybe I should wait until I can next actually use my rib (3 weeks time!) and then double check my WOT rpm with just me and also +1 person. If I am correct and its slightly too high at 6000rpm with just me (the recommended WOT range is 5150 -5850rpm) then I will be very tempted to go up to an 11 x 15 prop to lower my WOT rpm slightly. As we know all boats are different, maybe mine is slightly lighter or something and will react differently? Who knows!

Out of interest what did you do with your stainless prop? lol

Cheers,
James.