Mariner 40hp 2 cylinder prop question

anzomcik

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I bought a mariner 40hp 2 cylinder motor 1990. It comeing without a prop. So I have no numbers at all, starting fresh.

It is going on a 14.5 foot aluminum side console boat, weighing about 1000-1200lbs loaded (thats a guess). The 25hp on it now pushes it 21-22mph with an 11 pitch four blade solas.

I am looking for anyone who has a motor similiar to tell me what pitch they are running (and kind of boat they have) so I can BALLPARK a prop for my rig.

I understand that all of this is mearly speculation, but there is no way to know what i should buy since I have nothing to make the boat move with now. This i felt was my best option.

I am thinking 14pitch 4 blade solas, but I am open to opinions
 

steelespike

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Re: Mariner 40hp 2 cylinder prop question

To do this right you'll need a tach and a gps for speed.
Does this boat have a full floor complete side console live well etc.
What year and brand of 25?
I think you should shoot for undersized prop If it ends up too light you can still use it by watching the rpm.
and it will deliver lively performance.
Your 14 guess is in the ball park but may be on the high side.
If you do end up to high a pitch you shouldn't run it too much unless its just slightly out.
it may be sluggish.
 

anzomcik

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Re: Mariner 40hp 2 cylinder prop question

I have no numbers at all for the 40 because it has no prop so establish a base line.

My boat is 14.5 side console full floor front and rear casting deck two group 31 batterys 11 gallon fuel tank 4hp kicker and bowmount trolling motor and fishing equiptment. So all of my rough addition with me and my buddy it should be in the ball park of 1000-1200lbs.

Motor that is on it now is a 1988 mariner 25 hp, 2.25:1 gearing solas 11pitch 4 blade gps is 21-22mph with the full load running 5600rpm

If I had a rpop to run it with I would be able to figure it out with no problem, but since it is starting from scratch I am asking for thoughts.
 

pootnic

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Re: Mariner 40hp 2 cylinder prop question

You said the length and possible weight,what type of hull,flat,semiV,deepV?
I had a 40hp Suzuki on a 16.5' boat 6 degree deadrise so pretty flat used a 13 pitch when loaded and a 15 pitch by myself.
Why are you thinking a 4 blade prop,(plane quicker),it might be perfect?
 

anzomcik

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Re: Mariner 40hp 2 cylinder prop question

Semi vee no more than a 6 degree dead rise, never measured, but definatly not flat.

I like four blade props, I did alot of testing of props with my 25hp and the four blade gave me the best combo of speed handling and holeshot. Also the Solas amita 4 did not lose any RPM going to the forth blade. So a four blade is my person preferance.
 

steelespike

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Re: Mariner 40hp 2 cylinder prop question

Not sure why you went through that long explanation about no prop it was pretty obvious.
The reference to a tach and gps is to be sure the prop you select is right and be able to tell what change if any.
Nothing wrong with a 4 blade they do a nice job.
keep in mind a 4 blade will usually knock a little of the top.
 

pootnic

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Re: Mariner 40hp 2 cylinder prop question

4 blade might be fine,probably loose some top end but will plane quicker.
Your 25hp was is on the smallish side so the 4 blade may have been needed.With the 40hp a 3 blade maybe fine and give you a few more options.
 

jestor68

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Re: Mariner 40hp 2 cylinder prop question

The Mercury prop selector came up with several options in 13 pitch, including their 4 blade "Spitfire" aluminum prop.

Solas does have a 10.5 X 13 Amita 4 blade available right here at iboats.

I love it when a plan comes together. :)
 

anzomcik

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Re: Mariner 40hp 2 cylinder prop question

I got to run the boat tonight with the repower.

I am a little mixed on the results.
Average top speed GPS: 27mph (26-28 range depends on wind and waves)
WOT average: 4400rpm
Prop 14 pitch Solas Amita 4 blade
Slip: 9%
Antivent plate is 1 inch under the bottom of the hull.

The boat drive excellent, no venting in hard corners, tracked good no suprises or wierd spots. Only comment was the motor seemed a little labored when it was getting going.

I really liked the slip being under 10%, I liked the speed in the upper 20s. However The 4400 rpm threw me. My tach seemed to be working fine as my idle was 900rpm (tiny Tac) My WOT range is 5000-5500.

So I did some math by the time I get a lower pitch prop to get in the the range my top speed will be right near where my 25 was pushing me, lower 20s. Also does it seem correct that I would need a 10 or 11 pitch prop for a 40 when my 25 was swinging a 11 pitch well? (i understand the gearing and prop diameter are slightly different) Remember this boat is what i feel is a light load for a 40, especially since my 25 did very well with it.

Anythoughts on my results?
 

steelespike

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Re: Mariner 40hp 2 cylinder prop question

I think verifying your tach is easier than checking your motors state.
If the tach checks out then go through the motor with a compression check,Throttle opening all the way
Link & sync right.etc. If the tach is right you have to make up at least 1100 rpm.Can't really do it with a prop.
I think A 1200lb boat with a 14" prop should be able to turn 5500 rpm. at least about 30 mph.
There is the possibility that a smallish boat might not have the footprint to get up 1200 lbs on the water.
I forgot your running a 4 blade so that might soak up a couple hundred rpm.If you raise the motor you
might gain a little more rpm and speed. If you have no venting at all your probably too low.
The 4 blade should allow maximum height.Might be good to go over the setup before too much motor investigation.
 

anzomcik

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Re: Mariner 40hp 2 cylinder prop question

I check motor compression before i even started it. 135 both cylinders. with the plugs out i hand turned over the motor with it in gear turned over smooth nothing seemed to have any huge drag in the drive train. Also i verified it is a 2:1 lower unit, by turning over by hand.

The has a 65inch beam so its foot print is I think fairly large for a 14.5 foot boat. I was alone yesterday so that saved 200lbs on the weight I estimated before.

The carbs have a baffleing/filter set up on the opening so being able to look in to verify if they are infact wide open I can do. But the linkages are both as far open as they can be.
 

anzomcik

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Re: Mariner 40hp 2 cylinder prop question

I went and got a 12pitch Solas Amita 3.

Kinda puzzling with the results. Previous post on this thread tells I was having troubles with the 14ptch 4 blade, so the new prop is an extreme opposite

Witht eh 3 blade 12 pitch I have a super great hole shot, less than 3 secounds I am on plane, at about the 5 secound mark I am bouncing off the rev limiter.

So my numbers are 28mph at 5500rpm, it would go more, much more but it is governed electronically.

So what do you make of this.
14pitch 4 blade 4400 rpm 27mph
going to
12pitch 3 blade 5500+rpm 28mph

Is it me or is somthing not quite correct?
 

pootnic

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Re: Mariner 40hp 2 cylinder prop question

Without looking at the 4 blade prop results,it seems to sound about right.I mentioned earlier what I used on a longer boat so a 12pitch hitting the limiter seems possible,especially if this was the first prop you tried.

Maybe I did the prop slippage wrong with the 4 blade 14inch but I get 3-4%,which seems alittle to low...maybe it isn't but doesn't seem quite right.Which prop calculator did you use?
 

anzomcik

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Re: Mariner 40hp 2 cylinder prop question

With my 4 blade 14 pitch, I was 4400rpm 27mph with a 2:1 gear ratio that is about 9% slip
Thats 600 rpm below the 5000-5500 WOT range.

I expected the 12 pitch to be 5000-5100 by the rule of thumbs, losing 1 blade and two inches of pitch should have gained me 600rpm.

Instead I picked up +1100rpm with the rev limiter stopping the gain at 1100rpm. I got 28mph 5500rpm still the 2:1 ratio puts me at 10% slip

That is about double the gain i expected. It also takes me to the rev limiter fast.
 

pootnic

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Re: Mariner 40hp 2 cylinder prop question

Yeah...my fault used a different prop calculator,went back to my normal one,had around the same results as you.

Your logic seems fine with the information giving,in regards to the size prop you chose.
I guess it goes to show it's not an exact science and maybe with changing the blade style,plus pitch was to many varibles to make it work perfect.It did get you in the ballpark and now it's trial and error to you get the best one.

I'm using a 30hp Mariner (86 yama made) currently,on a crestliner 1652(10 3/4 pitch heavy load;13 pitch mostly)

I'm alittle surprized your motor wouldn't spin that 14P at the right rpms and to have a pretty good speed and slippage...but if you put the 12P on first I wouldn't have been surprized that you hit the limiter.I know this doesn't help your problem,hopefully you can exchange one of those props for another to try...
 

steelespike

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Re: Mariner 40hp 2 cylinder prop question

With my 4 blade 14 pitch, I was 4400rpm 27mph with a 2:1 gear ratio that is about 9% slip
Thats 600 rpm below the 5000-5500 WOT range.

I expected the 12 pitch to be 5000-5100 by the rule of thumbs, losing 1 blade and two inches of pitch should have gained me 600rpm.

Instead I picked up +1100rpm with the rev limiter stopping the gain at 1100rpm. I got 28mph 5500rpm still the 2:1 ratio puts me at 10% slip

That is about double the gain i expected. It also takes me to the rev limiter fast.

You no doubt know more about a 40 hp Mariner than I do; but I've never heard of a 40 hp 2 stroke outboard with a rev limiter.
Especially a 22 year old motor.
There really isn't a need for one as there is no possibility of valve float. causing damage.
Also its highly unlikely it would cut in exactly at its 5500 rpm max rating.
No doubt something is limiting it but I think maybe fuel flow or an ignition shortcoming.
I wonder if the same problem may have held it back at 4400 that held it back at 5500.
With the 12" prop it was easier to get to 5500 so the problem arrived at higher rpm
but perhaps a similar load.Note the same speed.?
 

anzomcik

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Re: Mariner 40hp 2 cylinder prop question

You no doubt know more about a 40 hp Mariner than I do; but I've never heard of a 40 hp 2 stroke outboard with a rev limiter.
Especially a 22 year old motor.
There really isn't a need for one as there is no possibility of valve float. causing damage.
Also its highly unlikely it would cut in exactly at its 5500 rpm max rating.
No doubt something is limiting it but I think maybe fuel flow or an ignition shortcoming.
I wonder if the same problem may have held it back at 4400 that held it back at 5500.
With the 12" prop it was easier to get to 5500 so the problem arrived at higher rpm
but perhaps a similar load.Note the same speed.?

I can get my tach to read 5450 with out the cutting out sound. Any more fuel to the motor I get no higher on the tach, the tach will fluxuate from 5300-5450 in combination with the motor cutting out sound. That isnt present with the 4 blade 14 pitch.

I can see the similatites with the 28mph. But at 5450 (the tach has a lcd screen) The motor with out a doubt has the ignition limiting further rpms. The sound is spot on to other motors (not just outboards) that I have heard hit the limiter
 

steelespike

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Re: Mariner 40hp 2 cylinder prop question

Makes no sense to me for a rev limiter to cut in before the motor reaches its wot rpm.
 

anzomcik

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Re: Mariner 40hp 2 cylinder prop question

My max WOT is 5500, my tach will read 5450. My opinion that tach reading is close enough to 5500, it is only 1% off, to say the rev limiter is at 5500rpm.
 

steelespike

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Re: Mariner 40hp 2 cylinder prop question

I'll try once more, compare our total posts which of us is likely to have more accurate information?
First you don't have a rev limiter second it wouldn't be set at 5500 more likely 57-5900.
Not trying to prove I'm right ,trying to get you to try to figure out why your motor acts up at 5500.
I had and operated alone my first boat when I was 6.I've had 10 vintage inboards that I either restored and or operated
over the years,also 13 outboard motors I personally worked on and operated over the years and presently have a 5 outboard
collection I'll be fiddling with this winter.
 
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