Tiki Pontoon with 80hp mariner - prop selection?'s

[mcurcio1989]

Boat in the picture ? I built this boat a few years ago It has 4 pontoons 2-25? toons on the outside and two 20? toons on the inside. I first threw an old 40hp Johnson on it that ran awful. Then I bought a 1980 80hp mariner but there were carb issues and lower unit issues that prevented me from running it until now. I had put 20hp mariner on there that ran like a freaking champ until I could fix this one. It was way underpowered. I finally found time to rebuild the lower unit and I tuned the engine in the water, under loads, yesterday and she is running good.

It has a beat up old aluminum prop on there. I want to replace the prop but I am not sure what to get. With the existing prop it will do 18mph with just me on there. The boat drags like a ton of bricks in the water ? soon as you remove power it?s like you?re pressing the brakes. Typical usage for this boat is me and 13 friends going to the sandbar (main reason I got this motor was because it has power trim) for a while and then head 4 miles to the docks downtown to grab food or go to beach volleyball. So I think I really need something with low pitch ? only question is how low and would I be wise to get 4 blades?

I am leaning towards 4 as I need good responsive power when docking as usually I don?t have good assistance. I liked the fuel sipping nature of the 20hp mariner but when I had a boat full of people it topped out at about 5mph. So am I a good candidate for 4 blades and how low would you go as far as pitch? One calculator said 13-14? but the lowest most props come in looks to be 15?

Also I am thinking stainless, again to help it bite at low speeds but also because our bottom is very muddy and has lots of little sticks. It eats up aluminum props but stainless cut right through everything. Obviously, I don?t plan to touch bottom but I do find myself in shallow water often. Any other thoughts there

 

[mcurcio1989]

Also if you want to recommend a model feel free - This isn't an offshore racing boat here I don't need anything too fancy.

So I guess my initial thought is-

stainless
4 blade
13.8" (or around there) diameter
13" pitch (due to my heavy passenger weight)
RH of course

your thoughts?


One thing I am confused on is that mercury's calculator says pontoon should be 13.45" pitch and max out at 18mph while tritoon should be 15" pitch and max out at 26mph. I have 4 toons (I need to check the prop that is on there as I don't what the pitch is) but I do know that right now I'm at 18mph and being that the motor cam off of a small runabout I'm sure it has like an 18-19" prop or something on there. I know tri's are supposed to be faster as the engine doesn't have to work as hard to keep them on plain but my boat just seems to not reap those benefits.

 

[steelespike]

A 4 blade should help with overall control especially around the dock.
A stainless should hold up better with mud and such.
But I think for testing a 13" 4 blade al prop till you see what size works.
Unless you can find a dealer that will let you try props with the understanding your buying and a sizable deposit.
It appears that your Mariner and a 1980 Yamaha are the same prop maybe the same motor.
To do this right you will need a tach and a gps for speed.
Looks like the tube diameter is small.
Sure looks low at the stern.
I think todays toons are at least 24 , 25 inches.
What is visible looks small.
I think that a 24 ft 2 tube toon with a healthy 80 could make 20-24 mph.
Keep in mind that pontoon speeds are all over the place for no obvious reason.
Looks like you may be dragging some of the under side through the water even with a light load.

 

[mcurcio1989]

My toons are the smaller old style but this is a Quadtoon. It is a 4 tube toon, I built it like that for extra flotation. The middle two toons are 4' shorter to give clearance around the engine / mount. I hear you on testing I may need to do that. with the aluminum props. I have a gps on my phone but I need to add a tach.

 

[steelespike]

My toons are the smaller old style but this is a Quadtoon. It is a 4 tube toon, I built it like that for extra flotation. The middle two toons are 4' shorter to give clearance around the engine / mount. I hear you on testing I may need to do that. with the aluminum props. I have a gps on my phone but I need to add a tach.

I understand it is a quadtoon.It does help your flotation but your underside is closer to the water. probably not as much room between water and underside to start with. Yours is a pontoon that bright benefit from an under skin.
Usually on a toon we don't worry much about dragging a little extra motor through the water but if your dragging an extra 6 or 8 inches it might pay to raise the motor a ltitle at a time to a point just before ventilation becomes a problemBy the way;.Your present prop size is probably under the prop nut.
Don't do 2 changes at once get your prop and test well then consider other changes.

 

[mcurcio1989]

Oh okay, I see what you're saying now. The motor is one notch below the point where it ventilates. So, If I put it any higher it will ventilate.

I'm sure there is some spray hitting the underside but the two center toons are touching and there is only maybe 5" between the outer toons and the inner toons on either side. I don't know if an underskin would do all that much but it isn't even an option since I can't really even reach my hand up there to attach anything.

I'm thinking I will get a 13" 4 blade aluminum prop to test and see what pitch works best. I will either try a 15" or 13" first depending on what pitch I currently have.

Thanks!

 

[steelespike]

When you get the new prop you may be able to raise the motor a little.

 

[mcurcio1989]

Well I haven't had a chance to check what prop is on there, as the engine doesn't tilt up enough to get the prop of the water, but I went ahead and ordered a Solas Amita 4 blade 13.25" diameter 13' pitch aluminum. We'll see how that works. I think if anything I would probably want to go down in pitch (which isn't an option) so I think this will be my best bet. I'll report back on how it works out.

Assuming this does the job, I'll run this one until it needs repaired and then I will replace it with the same prop but in stainless.