Mariner 115 - Pitch Change?

[tedder]

Smashed up my prop yesterday. Looking into a replacment and could use some input.

Boat - 17.5 Alum Smokercraft
Motor - 1996 Mariner 115

WOT (estimate since I have not run the boat much) is 4800 maybe alittle higher.
Currently running a 19 pitch (I think its the original prop!!)

I noticed when loaded with fuel, 4 people and gear she takes longer to get up and going. Since I normally would carry 3-4 people and lots of fuel and
gear should I and can I move to a 17 pitch?

Also, I have a chance to buy a 15 pitch at a really cheap price. Should I buy it as a 3rd spare for the heck of it and will
it fit my motor and will it be of any real use to me. The part# on the 15 pitch prop is 48-77342-15 if that means anything.

Lastly, I am wondering about the props with the hub assemblies.... like this one
http://www.iboats.com/mall/propfind...3862&cart_id=551369825&engine_id=289&pf_new=1
when damaged do these props spin freely and totaly disable the boat, are these the better way to go or should I go with one like this one
http://www.iboats.com/mall/propfind...3862&cart_id=551369825&engine_id=289&pf_new=1



Cheers

 

[Texasmark]

Re: Mariner 115 - Pitch Change?

'94 sales brochure says your WOT is 4750-5250. You are ok, but people perfer to be at the top of the range.

Gearbox is 2.07:1 if anyone asks.

4 people and all their goodies is a good load so you are interested in plenty of torque; hence the lower pitches which will help your hole shot also.

I just bought a Hustler prop ((they're high performance aluminum) with the removable hub and it seems to be ok. They advertise that if you ding the prop you can just buy the replacement prop and save the $30 cost of the hub.

The hub looks ok, but it is not rubber and not a slip hub and it looks like the prop will sacrifice, not the hub slip if you hit something of any size like most rubber hubs are designed to do.

If the same hub (type) is used with SS props, then you will probably shear the hub if you really whack something. Just food for thought as the hub has plastic and brass in it and if you twist it you are going to push against the brass and if you continue to twist it you will shear the brass and then it will slip.....permanently.
--------------------
I'm going to jump out and say go to the 15 and try it before you buy the 17. You may find that you are very happy with it and don't need the 17.

You will notice a significant gain in hole shot but will loose some top end.

Just ran some BAM prop slip calcs and here is an idea of what it will cost you.....guessing at 20% prop slip which, with that load is probably pretty close.....but just a guess (sorta educated). Grin (The 0% slip is an imaginary number for calculation purposes which would assume the prop were turning through a solid, which it is not.)

Current 19P 4800 rpm, 43 mph @ 0% slip, @ 20% slip WOT= 34 mph.

Proposed 17P 5000 rpm, 40 @0% slip, @20% slip WOT = 32
Proposed 15P 5200 rpm, 37 @0% slip, @20% slip WOT= 30

So, for the improved WOT operating rpm's, hole shot, and slower speed improvement in handling, I doubt that you will notice the WOT speed difference between the current 19 and the 15, and if you did notice it you probably would readily accept it.....from what you've said. Plus you don't have to buy another prop and the numbers will probably be better than indicated.

Good luck,

Mark

 

[walleyehed]

Re: Mariner 115 - Pitch Change?

The only flaw I see in that suggestion, Mark, is we're in the lower region of the powerband now, and 2" pitch change will likely be from 4800 with the 19, to close to 5200 with the 17, maybe even 5300.
I think you'll see close to 5500 with the 15 if blade design is simular.
1" pitch change will be close to 200RPM.

 

[Texasmark]

Re: Mariner 115 - Pitch Change?

Kenny, right again. After all that trouble I later realized that I used 1" pitch change vs rpm in my calcs rather than 2" which would have made my numbers closer to yours. You'd think one would realize that changing from 19 to 17 to 15 are changes of 2" not 1" and corresponding rpm changes of 400ish not 200.....oh well!

Sorry and Sorry Tedder. At least you get the idea.

One thing about your 15 (after looking at it again) you may suffer whiplash on your hole shot. LOL

Glad we keep each other honest and accurate. Grin.

Mark