40 HP Nissan on a 24 foot pontoon info.

[JeepinGunGuy]

I picked up a new to me 2000 24 foot pontoon with a 40 HP Nissan, the prop is pretty ate up and has no identifying marks on it. I would like to get a replacement prop since this one bogs the motor at 4500 rpm at WOT. The WOT spec for the motor is 5100 to 5700. Do any of you guy's have a similar setup? I'm just looking for an educated jumping off point since I have no clue where I am starting from. Thanks in advance.

 

[Sea Rider]

If don't know which pitch is current damaged prop will need to take it to a prop shop and have it measured. Probably is the one factory delivered with motor which should be a medium pitched one for light to medium light applications. Nissan's are rebadged 2 stroke Tohatsu motors.

How loaded was the toon when achived just 4500 wot rpm , plan using it with same number of sould on board but with a new prop installed ? Once the current pitch and load is known will be much better selecting a less prop pitch to pull wot revs middle to max wot rpm range factory stated, will power toon more efficiently to be on its way faster.

Happy Boating

 

[JeepinGunGuy]

If don't know which pitch is current damaged prop will need to take it to a prop shop and have it measured. Probably is the one factory delivered with motor which should be a medium pitched one for light to medium light applications. Nissan's are rebadged 2 stroke Tohatsu motors.

How loaded was the toon when achived just 4500 wot rpm , plan using it with same number of sould on board but with a new prop installed ? Once the current pitch and load is known will be much better selecting a less prop pitch to pull wot revs middle to max wot rpm range factory stated, will power toon more efficiently to be on its way faster.

Happy Boating

Any clue where the factory pitch stamping would be? It's not on the outer hub or between the blades like most. It does say Nissan on the hub. I took it out last night with just me and 2 grand kids 400 pounds total the day before I had 1500 pounds total. in both cases the motor stopped around the 4500 RPM range, the only difference being at 400 pounds the prop would blow sucking air and the rpm's would spike. This is a big fat pig and I have no delusions that it will be a speed demon I just need something to put the motor at the right rpm to give it all the help it can get.

 

[WesNewell]

Without more info, like engine year/model, pontoon weight, I'd suggest you get the less pitch available. Such a small engine on a 24' pontoon isn't going to get you much speed. A 7-8P 4 blade would probably be your best bet.Might try the mercury prop finder. Using a 2001 Nissan 40hp and 3000# for pontoon weight, it suggest an 8P prop.
https://www.mercurymarine.com/en/us/propellers/selector/#!/step-one

 

[Sea Rider]

Motor year is irrelevant, model is all. If the stamped number isn't shown on the prop body, blade or at front of the prop hub better take it to a prop shop and have it measured, should be doing that by now LOL!!

Will the toon be used with a fixed or variable load, say a 4 member family. The issue is that with underpowered motors adding to much load after the motor has been maxed prop to run towards its full wot revs with a fixed load can turn unproductive killing what was already achieved.

The lower leg of that model has a tall plate, if the prop aerates when sitting at 90 deg and the toon was well deck balanced will surely need going for a motor/transom optimization which traduces to a incoming water flow/lower leg match for top prop thrust. Does the toon counts with a variable height transom or it's fixed ?

If counting with a installed tach would be better to know current prop pitch, it's a bad idea playing with pitches wild guessing when the current one isn't known. Don't know if Merc had same rebadged model in use, if not their Prop Selector will turn useless.

Tohatsu counts with severeal nice OEM props you can go for after for motor to run towards its max 5800 wot rpm range, at just 4500 as loaded need an extra 1300 wot revs which could be achieved going towards 3 max less pitches from current one....

Happy Boating

 

[WesNewell]

Engine year is NOT irrelevant as gear ratios can and have changed from one year to the next in certain models. Not often does it happen, but it does happen.

 

[Sea Rider]

Really ? was missing your periodical wild guessing answers ? The M40 C has not changed a bit over the years since was released moons back. The ones that have serviced were found with same prop pitch which indicates the gear box ratio remained exact same....

BTW, the Merc prop calculaor doesn't list that oldie 40C under Nissan or Tohatsu motor brands....

Happy Boating

 

[Faztbullet]

Poster did not say what year or model so your wild guessing its a M40??? Could be a 40 TLDI or a 40 fourstroke and all three use a different gear ratio.

 

[Sea Rider]

Yep, I apologize for that 40 ? outburst, seems to much time locked in sanitary confinement. Being a 2000 year boat will assume that's been powered with a M40C or a M40D2 and not a newer MFS 40 TDLI model.

The OP should have stated the current NSN 40 model and color, with out that precise data won't be having summer fun time anytime soon as playing blindly with prop pitches could turn into a costly water experimentation....

The gear box ratio is not that important you can always prop a motor right to rev between middle to its max wort rpm range with a well selected prop for any given HP motor. Lots of props to play with...

Happy Boating

 

[Faztbullet]

The gear box ratio is not that important you can always prop a motor right to rev between middle to its max wort rpm

That is incorrect ...if it didnt matter the MFG would use same ratio on all models of same HP. Best example is putting a 2:1 ratio on a I4 that had a 2:3:1 ratio..Yes you can prop it to reach RPM spec but its a dog out the hole and low end is terrible.

 

[Sea Rider]

That is incorrect ...if it didnt matter the MFG would use same ratio on all models of same HP. Best example is putting a 2:1 ratio on a I4 that had a 2:3:1 ratio..Yes you can prop it to reach RPM spec but its a dog out the hole and low end is terrible.

You have to dial a nice prop to work with your current motor HP gear case ratio factory delivered with, you think that soon after each boater buys an outboard motor will go straight to change the current gear ration for a better one at an extra part cost and labor expense, no way.

Playing with gear ratios surely works much better in high end HP motors powering heavy boats. The gear ratio is what each motor manufacturer wants to put inside their respective gear boxes, why should all be equal between HP brands ? Work with what the motor's gear case ratio has already been installed with.

This is as pretending to modify the factory prop diam for other diam, simply stick with what the prop manufacturer wants to put in his prop and work from there. Stay simple why complicate your simple boating life with any other gear box ratio..

Happy Boating

 

[JeepinGunGuy]

Well I learned a few new things about the new toon. It's a 25 footer for starters, should weigh 2200 pounds. The motor is a 1999 40 D2EPTO. The transom is fixed mounted. There is not a prop shop within 100 miles of me that can measure my old prop. Would a 4 blade help with the prop aerating at all or would it aggravate the issue? Is there a post on here that covers how to measure a prop for pitch? I did a little searching but no luck.

 

[WesNewell]

Solas prop finder recommends a 5311-122-07. That's an Amita 3 blade 7P.. And yjay's in line with what I thought.

 

[Sea Rider]

In reality can install any prop, but it's a zillion times better if knowing the actual prop pitch and max wot revs the motor achieved as loaded and go from there. Can go per the prop finder suggestion, a 3 blade 7 pitch at your own expense and risk. Anyway, will need to buy a prop. Report the max wot rpm the motor achieved with said 7 pitch...

Happy Boating

 

[Sea Rider]

Found a Tohatsu M40D2 3 cylinder motor with a standard factory delivered OEM 11 pitch 3 blade prop , can go for a OEM 3 blade 9 pitch or a four blade 7 pitch, assume that with a pontoon boat a 4 blade will suit better ? The pontoon experts should have a clue..Being that Nissan a rebadged Tohatsu version should have a 11 prop pitch installed ?

Happy Boating

 

[JeepinGunGuy]

Found a Tohatsu M40D2 3 cylinder motor with a standard factory delivered OEM 11 pitch 3 blade prop , can go for a OEM 3 blade 9 pitch or a four blade 7 pitch, assume that with a pontoon boat a 4 blade will suit better ? The pontoon experts should have a clue..Being that Nissan a rebadged Tohatsu version should have a 11 prop pitch installed ?

Happy Boating

You are correct it did come with a 11 pitch 3 blade prop. I took the prop off and measured the pitch using this procedure MANUAL PROCEDURE FOR PROPELLER PITCH MEASUREMENT Then when I was cleaning and reshaping the prop I found an 11 stamped in it on the back side of one of the blades. I reshaped the blades tig welded in all the missing chunks and it still does not perform much better then when it was all beat up, still venting bad when the boat is loaded lightly and hits a wall at 4700 RPM now. I am now stuck in a dilemma where it looks like a 7P 4 blade prop would be my best option, nobody but the OEM made a 7P 4 blade and the only ones for sale are ridiculously priced. Based on this new information where would you go with this? I need 1000 RPM to put me at max WOT, do these 2 strokes prefer the higher revs like my old dirt bikes? Would the venting issues increase or decrease with a 4 blade? The motor is as low as it can go on the transom, the boat is rated for a 130 HP max motor according to the load sticker.

 

[ahicks]

First, a 4 blade prop will have less of a tendency to vent. I think most will agree with that idea.

Second, to get the motor on it's max HP curve will take a 1000 rpm increase. THAT's the hard part, especially when converting to a 4 blade at the same time.

Personally, I think a 7p prop is a pretty extreme low pitch. I think something like an 8 or 9p might work out better.

I would go with a Solas alum. prop.

Regarding the venting, is there anything that seems to provoke that? Like a hard turn, or running in swells? Maybe just full throttle from a standing start? What is going on when that happens? What are the chances you have too much weight or gear loaded forward? Anything that can be moved back?

 

[Faztbullet]

Its under powered and motor pod may be displacing water in front of prop causing venting.

 

[WesNewell]

The Solas Amita 5313-118.09 is a 9P 4 blade, but I think you'd be better off with the 7P Amita 3 blade 5311-122-07. Either can be had new for under $100. The 7P should get you into the recommended wot range. Doubt the 9p 4 blade will get you more than ~100 rpm more than your 11p 3 blade.

 

[Sea Rider]

The prop choice comes down to : 3 blade 9 pitch or a 4 blade 7 pitch, with a 3 blade OEM Tohatsu prop can achieve as much as 300 to 500 wot rpm increase with just one pitch decrease, depends on the hull type, lenght and current load of the watercraft. Know from experience messing constantly with OEM props.,.


Happy Boating