XL Shaft lengths

MattPark · 03-05-2010, 07:51 PM

I had a 150 Merc on my boat, XL shaft. The engine was mounted one hole from all the way down, and the cavitation plate was right at the bottom of the boat.

I put the new 115 XL 4 stroke on today, and with the engine mounted as far down as it will go, that plate looks about 3" too high. As near as I can tell, the prop will easily ventilate when the boat gets up to speed, if it's ever able to. If it were an XXL, it would likely be too far in the water, even when mounted as high as possible. Right now it looks like I'll need a setback or jack plate.

I'm really not happy that I have a new surface piercing outboard. I didn't put it in the water, but it doesn't look good. Why would one XL be a different length than another?

Green Machine · 03-05-2010, 08:38 PM

Short = 15 inches
Long = 20 inches
Extra Long = 25 inches
Extra Extra Long = 30 inches

All from cavitation plate to neck.

They should all be the same unless your old motor was truly old......

Out of curiousity, what is the length of your old motor? If you got a XXL, could you mount it on the bottom hole? A jack plate will fix the problem and help performance, but it sucks you may have to buy one!!

Keep us informed and good luck.

Green Machine

MattPark · 03-05-2010, 09:27 PM

Both are 25" as far as I know. The 150 was a 95, the 115 is an 04. The 115 is an EXLPT. Both engines have a 5" extension housing above the lower unit.

An XXL might work on the bottom hole, but I think it would be too low. I don't really want to buy another lower unit.

The thing that doesn't make sense is the difference is 3", not the 5" it would be going from a L to XL or XL to XXL. The difference between the top and bottom holes on the engine is 3.5", so even with the 115 mounted as high as it would go (bottom hole) the difference would barely be 5" from where the old engine was mounted.

I've been looking at jack plates, but it looks like they are mostly for raising the engine. Are there plates that have a lot of downward adjustment? Maybe I could mount one upside down?

budnate · 03-06-2010, 07:19 AM

wierd that dont make sense both are newer motors should be the same dont spose the yami guy stuck the wrong sticker on it??,

here is a pic of some brackets I saw online somehwere awhile back, jack plates go either way up or down when centered, go to CMC and see there unit it is bullet proof.

Green Machine · 03-06-2010, 07:09 PM

Quote:

Originally Posted by MattPark

Both are 25" as far as I know. The 150 was a 95, the 115 is an 04. The 115 is an EXLPT. Both engines have a 5" extension housing above the lower unit.

An XXL might work on the bottom hole, but I think it would be too low. I don't really want to buy another lower unit.

The thing that doesn't make sense is the difference is 3", not the 5" it would be going from a L to XL or XL to XXL. The difference between the top and bottom holes on the engine is 3.5", so even with the 115 mounted as high as it would go (bottom hole) the difference would barely be 5" from where the old engine was mounted.

I've been looking at jack plates, but it looks like they are mostly for raising the engine. Are there plates that have a lot of downward adjustment? Maybe I could mount one upside down?

Something isn't quite making sense.......both motors are 25", but one sits 3 inches lower than the other? If you still have the old motor, you might measure that versus the new one. I agree with Bud......maybe the Yami is a long shaft and meant to be mounted on the bottom hole?

I have had a jack plate before and they work great for dialing in the motor to the sweet spot, but you shouldn't need one unless your transom is an odd height.

Green Machine

Green Machine · 03-06-2010, 07:22 PM

Still thinking on this one......do you have any pictures of the new motor mounted?

Green Machine

MattPark · 03-06-2010, 08:16 PM

Heres the old motor mounted, second hole from all the way down. The cavitation plate is even with the bottom of the hull when the engine is lowered. I'm not at home, but as soon as I am I'll get a pic of the new motor (Merc 115).

The new four stroke is definitely a XL, hence the EXLTP. Both engines have the same 5" spacer visible in this picture of the old motor. The only thing that would make this all make sense is if I am mistaken, and the old motor (pictured) is a XXL, but it wouldn't explain the fact that it's only 3-3.5" different when mounted in the same holes.

Can I run a jack plate backwards to get the drop I need? I don't see why it wouldn't work, the holes would line up either way. I just don't see any of the ones I'm looking at having the drop I need when mounted "correctly".

Flatfish · 03-06-2010, 10:29 PM

A jack plate can lower it down some. I have had 2 boats with em on a tiller, and in both cases the tiller handle height was more or less what set motor height. That and the fuel/power conduit that goes into the motor.

Starfish · 03-07-2010, 05:10 AM

Very strange. But... before you give up and try a jackplate, be sure to mount it as low as possible and give it a try. It's often okay (and actually preferable) to have the cav plate a little bit above the bottom of the hull. If it performs okay but occasionally ventilates, try a stainless prop and see if that lets it keep its grip. You'll actually end up with better top speed that way than if you mount it too low.

MattPark · 03-07-2010, 12:19 PM

Here's how it's mounted. No more room to drop that I can find.

Heres a view from the rear, with the engine where it would likely be trimmed on plane.

Here's a view from the port side. 2/3rds of the water intake ports are above the bottom of the boat, when I put a straight edge up there. That itself seems like it could be a big problem.

I think I may have figured out the problem, correct me if I'm wrong. From the top of the transom to the bottom centerline of the hull is 30 inches. This XL 115 is a 25" shaft. My other motor (not here to measure) MUST be a 30" motor, and this one isn't going to work without modifications.

The reason I'm only getting about 3.5" difference may be because of this: "Mercury/Mariner 75 through 125: 20 inch (L) is 21 11/16 inches, 22 1/2 (LL) is 24 1/6 inches, 25 inch (XL) is 26 11/16 inches" which comes from the Mercury outboard rigging technical manual. This 25 inch motor is 26 11/16ths, so my difference can't be 5". I need an XXL or a jack plate cabable of a 4" drop.

Green Machine · 03-07-2010, 12:53 PM

Well, I'm not a mechanic, but I do believe while on plane the waterline will be all the way out to your chine. (Where the sides meet the bottom of the boat) Looks like you have a fairly deep "V", so I would take your straight edge from the chine and see how much higher it is than the keel. I bet it is close to 3 inches. So, that may make your cavitaion plate at the perfect height!!

But, maybe I am now confusing myself.......as a 30" transom is a XXL shaft. Hummmmmm, do they measure the transom heigth from the keel or the chine? I guess I would say if you have 30" sides and have a full height transom (not cut down), then you need a XXL. If you have 25" sides and full heigth transom, you are ok.

Green Machine

MattPark · 03-07-2010, 02:12 PM

I've got 30" sides, and a 10" cutout. The vertical distance between the chine and the keel is also 10", giving me a 30" transom.

MattPark · 03-07-2010, 04:17 PM

Just took it for a spin, it definitely needs an XXL or some kind of bracket. You can feel/hear the prop blowing out coming out of the hole, but it will actually plane and go just a bit over 30mph. Any kind of positive trim multiplies the problem exponentially. It feels like a boat with an extremely underpowered jet pump on it.

I'm thinking the 5.5" setback CMC ML-65 with a new set of holes drilled will do the trick.

Green Machine · 03-07-2010, 05:58 PM

The CMC is a good unit. Spend the extra bucks and get hydraulic, not manual. You can really dial in your motor on the water. (And if it is really rough you can run the motor a little lower in the water)

Green Machine

BerettaMan · 03-07-2010, 06:04 PM

Your old motor has a bay kit between the motor and the lower unit, it should be a 5" extension. This allows a Long shaft to work on a 25" transom and a XLS to work on a 30"". Your new motor does not have the Bay Kit. I just installed a Bay Kit on my 150 Yami, IM me if you have any questions

Jeff

MattPark · 03-07-2010, 07:44 PM

Thanks, Jeff. I knew there had to be a simple solution.

Flatfish · 03-07-2010, 07:47 PM

Side height does not matter. Transom height does.

By the looks of things, your old motor was an xxl, and your new motor is an xl.

I am not aware if they make a 115 with a 30" lower unit.

So your choices are-

1-xxl lower unit if available
2-Jack plate w/present lower unit(Assuming it is gonna clear enough to make the necessary amount of drop.)
3-Maybe a bass/hi pro shop makes a low intake for your new motor????

If your boat is a tiller, this will mandate that you have a 6" offset jack plate. If it's a windshield/console, then you could go with a deeper jack plate in an effort to let the water rise above the bottom of the hull in order to feed the intake.

PS-A 4" drop sounds pretty big. Do your homework before moving on.

MattPark · 03-07-2010, 08:23 PM

Bay Manufacturing lists a 5" extension kit for my engine.

Flatfish · 03-07-2010, 08:37 PM

Then it sounds like you have at least one option.

MattPark · 03-08-2010, 11:52 AM

Bay makes the extension, but not the 5" stub shaft for my engine, and the longest shaft Mercury makes for the 115 4 stroke is 25", which I already have.

Cutting down the transom (not gonna happen), an offshore bracket (probably not gonna happen), or a jackplate (highly likely) are my options with this engine. The low intake is not an option, my prop is just too high out of the water to function correctly.

smalldog · 03-08-2010, 07:18 PM

Sounds like you bought the wrong motor.

MattPark · 03-12-2010, 07:22 PM

I put a 5.5" hydraulic CMC jack plate on, and it's perfect. I'm even able to move it up some, which I didn't think I would be able to.