Propping a 2002 Johnson 115

[SailorChlud]

Hello, all:

I am looking at installing a 2002 Johnson carbed 115hp motor with a good service history, lower hours and overall good condition, on my 1972 Seafari. 25 inch shaft. The motor is a one-owner, dealer-serviced unit on a trailered (not wet stored) boat.

Does anyone have a suggestion for an aluminum prop (or stainless)? The model number is J115 PXSNF

Any thoughts on this motor for overall reliability? Fuel consumption? Concerns or weak points?

Thanks in advance for the help.

[Capt Chuck]

I have the same motor '05 Johnson 115HP Carb
I'm using a S/S Viper type prop 13.375 X 17 on my 18' Skiff. A lot of power. Fuel consumption will be different on your SeaCraft Hull. No major problems.

[Bushwacker]

That's a BRP-built motor, so should be very good quality. Don't know what power trim units they were using back then, but the V-4 E-TECs use the same trim system as the I-3 60/75/90 hp models, and they seem to have more problems than the triple ram units used on the V-6 models, so I'd take a close look at the trim system, i.e., corrosion on the trim motor housing and check to see how well the wires are sealed coming out of the PT relay. (It's about the size of a small match box on stbd side of motor if it's like an E-TEC.)

As for props, the 3B 13 3/4 x 15p OMC SST was a very good prop on my Seafari with the old 300 lb cross-flow 115 that probably wasn't more than about 100-105 hp at the prop. It would plane at 12 mph, burned about 8 gph @ 20 kts/23 mph/4500 rpm cruise (2.8 mpg) and run at least 32-34 mph/5500 rpm @ WOT with a very heavy load. That looper motor should be stronger and might be able to spin a little bigger prop, but I'd start with 15" pitch. I have an old Michigan 15 3/4 x 15p aluminum prop you can try. Make sure you get the motor height correct before you start screwing around with props; AV plate should be above solid water when you're up on plane like the pic below. I think I'd start out with it about 3/4" above keel. The Viper is BRP's very efficient bow-lifting speed prop and might give you the most WOT speed, but both Vezo II and Rickg couldn't get a Viper to hang on plane below about 22-23 mph! Low speed planing is real important if you run offshore very much, so depending on how much load you carry, a stern-lifting prop might be a better choice. I believe the SST II is a newer version of the prop I had, but once you get some initial test data, I'd consult Ken at PropGods, who would be more up to speed on the latest props.

[SailorChlud]

Thanks, Chuck, and Bushwacker.

I appreciate the offer of a loaner prop, Bushwacker, but I am reluctant to have you go through the trouble. The dealer has a selection of props to try out too, so I will start there.

In your reply you suggested a mounting height of 3/4 inch above the keel for the AV plate, but in other posts I have seen owner recommendations to try a bit higher - 1.5 inches? I need to instruct the dealer where to put the mounting bolts to give me some adjustment room, so should I use 3/4 inch as the lower bound, and 2 inches as the upper?

[Bushwacker]

Originally Posted by SailorChlud

. . . In your reply you suggested a mounting height of 3/4 inch above the keel for the AV plate, but in other posts I have seen owner recommendations to try a bit higher - 1.5 inches? I need to instruct the dealer where to put the mounting bolts to give me some adjustment room, so should I use 3/4 inch as the lower bound, and 2 inches as the upper?

How high you can run the motor really depends on the prop, as some props can run higher than others depending on how much cupping they have. I originally mounted my 115 with the plate flush with the bottom, but when I bought the SST prop, they said I could raise the motor 1 hole (3/4"), so I did and I picked up about 3 mph! This was way before I learned up about getting AV plate on top of clean water, so I don't really know if the AV plate was above clean water on my 115 set at 3/4". I just know that it ran much better there than flush. May have been able to run it even higher, but I never tried that. I did notice that I had to run with the motor trimmed down more to keep the prop from blowing out in rough seas, so I'm sure raising it more would have made that worse.

If your motor is like my E-TEC which has 4 holes, spaced 3/4" apart, if you mounted it so AV plate is flush when mounted in top hole (No.1), that would give you the following options on AV plate height:
Hole # - AV plate height
1 - 0.0
2 - 0.75"
3 - 1.50"
4 - 2.25"
Seems like this would be fairly conservative but still give you a decent range of heights and allow you to run anything from a cheap aluminum prop to a radical highly cupped prop. If you plan to only run a good SS prop, you might be able to set 0.75" as the min height.

Capt. Terry went through this on his Seafari in the last year or so and said his AV plate is on top of the water, but can't remember if he's at .75 or 1.5" height, as I think he's tried both settings, so we need to get Terry's input on this.

[Capt Terry]

Originally Posted by Bushwacker

Capt. Terry went through this on his Seafari in the last year or so and said his AV plate is on top of the water, but can't remember if he's at .75 or 1.5" height, as I think he's tried both settings, so we need to get Terry's input on this.

Just checked my records. After Skippertee observed my A/V plate underway and said it was good, I remeasured it 1.5" above keel. Hard to get a precise measurement on my trailer; previously measured about 1.75" in same position. I am in hole 4, as high as engine will go without more drilling. I am also about 2.0" from top of my 20" transom to the engine.

[Bushwacker]

FYI - Terry has a 20" shaft motor on a 20" transom, but if you have a 25" shaft motor and 25" transom, the bolt hole/height relationship should be the same. I believe most dealers have a template or jig for drilling the bolt holes relative to the cutout height. If you'll PM me an e-mail address, I can send you a .pdf file of a 96 page E-TEC installation guide which contains a lot of good info, including a drawing for where to drill the mounting holes in the transom!

[SailorChlud]

Thanks, gents, sounds like good advice. Bushwacker, PM sent.

[Bushwacker]

I just ran across this article on mounting height and prop testing which includes some really good info!

[SailorChlud]

Wow, that was very informative. Maybe worth a sticky?