Prop help-1993 Mariner 30ELO on a 16' toon

[Floo420]

Hi
New to the forum. I've read about as much as I could find on prop sizes for pontoon boats but most speak to large motors on big boats. I have a 16' 1990's Manitou (model unknown). I'm guessing it's in around 13/1400#'s. I've just got a new (to me) 1993 2 stroke Mariner 30ELO mounted this weekend and it felt like it was missing it's top end. In researching I've come to the conclusion that it's most likely got the wrong prop for the boat. Currently it has a "3814R 9 7/8x13 " mounted on it. I'm back in the city (Toronto) so I can't speak to the RPMs that I was getting, but will investigate that next weekend. I was hoping to try something different when I'm back up next weekend and was looking for suggestions.
Thanks in advance.

 

[jlh3rd]

it appears your motor's WOT rpm range is 4500-5500 . Your prop appears to be a 3 blade quicksilver 9 7/8 in. diameter x 13 in. pitch.
so, we need your WOT rpm's currently. The # of blades, diameter , and pitch plus the weight in your boat (people) all play a roll in what rpm's the motor reaches.
This is assuming your motor is healthy......is it?
Propping a boat can get expensive if your just guessing. Read up on it.

 

[Floo420]

Thanks @jih3rd. You're correct, that's what I have. The motor runs perfectly once it's going. I just installed it and I have a crappy fuel line which causes me to flood it more often than not. I don't have the current RPMs, but will get that this weekend. With respects to weight, I normally have @500#'s of ppl and gear total. It's mostly a boat to run around a small lake and fish on.
Since I only have a few weeks at the cabin left I was going to head up with a 10 * 9p this weekend to judge the difference and see what RPMs I get from that. Do you think that's a decent starting place?

 

[jlh3rd]

Since you already have the props, sure, it's as a legitimate starting point as any.
Understand that the 9p prop .....the diameters of both are practically equal.....is going to give you around an 800 rpm difference higher at WOT. You want to keep WOT rpm's around 5500.
Basic rule is 200+/- rpm for each inch in pitch change.
I'm gonna repeat, read up on propping a boat.
I can't tell you what will work exactly as I do not have your boat or motor.

and I haven't mentioned proper motor mounting height yet. That can affect propping.......read up.

 

[Floo420]

I've found another option in my research. It's a 48-42738 -A10 : 12.5 * 8P
This reads as the correct prop for the motor on a pontoon. There is a used one locally for $40 so I'm not heavily invested if it's not great. There is a pontoon version which has the suffix CP1 at the end. If this one is good I may try the cupped version.
The motor is hanging as low as possible, it's a long shaft so I don't see what more I can do there. Thanks again for the tips and help.

 

[jlh3rd]

sigh....

 

[airshot]

I've found another option in my research. It's a 48-42738 -A10 : 12.5 * 8P
This reads as the correct prop for the motor on a pontoon. There is a used one locally for $40 so I'm not heavily invested if it's not great. There is a pontoon version which has the suffix CP1 at the end. If this one is good I may try the cupped version.
The motor is hanging as low as possible, it's a long shaft so I don't see what more I can do there. Thanks again for the tips and help.

No one can say what prop you will need ! You can guess and experiment all you want, without accurate numbers for RPM and current prop specs, it is nothing but a guess ! Guess wrong and you will be replacing your motor !

 

[Floo420]

No one can say what prop you will need ! You can guess and experiment all you want, without accurate numbers for RPM and current prop specs, it is nothing but a guess ! Guess wrong and you will be replacing your motor !

Thanks for the reply. The intent really was to go back up north with some new options so that I have an alternative when I do measure the RPMs. Although you are correct and the input I'm looking for is just a "guess", some great feedback has put me on the right path.

 

[Chris1956]

On a related subject. Why is your crappy fuel line causing the motor to flood? How do you know it is flooding?

 

[Floo420]

That a good question. The bulb is faulty, the check valve is shot. So I end up over pumping. That in combination with just learning how the electronic choke button on the controls works has caused me some frustration. I've got the right sequence figured out now (as well as a new line).

 

[Chris1956]

A faulty check valve in the primer bulb would tend to not fill the carbs with fuel, rather than flood the engine. Most 2 cycle motors are pretty resistant to flooding. You will want to replace the primer bulb, however.

To start that motor, pump the primer 'till hard. Lift cold start lever, hold choke button and crank motor until she starts. Now use choke a bit now and again, if she needs it (most don't), until she is warm. You do not usually need any choke for a restart, after she is started for the first time that day.

If the primer bulb doesn't hard, you may have an issue with the carb inlet needle and float.

 

[Floo420]

A faulty check valve in the primer bulb would tend to not fill the carbs with fuel, rather than flood the engine. Most 2 cycle motors are pretty resistant to flooding. You will want to replace the primer bulb, however.

To start that motor, pump the primer 'till hard. Lift cold start lever, hold choke button and crank motor until she starts. Now use choke a bit now and again, if she needs it (most don't), until she is warm. You do not usually need any choke for a restart, after she is started for the first time that day.

If the primer bulb doesn't hard, you may have an issue with the carb inlet needle and float.

Thanks Chris.
The bulb didn't pressurize the line. That resulted in my over pumping it, that led to the flooding.
Appreciate your other tips.
Shawn

 

[Floo420]

Just a follow-up.
I took my "new" prop up north but with poor results. Despite multiple sites (and a shops confirmation), this prop would not even fit in the boat. The 12" Dia is too big. There is only 6" of space from the spine and the upper plate (which I'm sure there is a name for). Also the diameter and depth was too big.
Looks like I'm going to have to try the 10" 10P version and use that as a starting place for.my RPM results.