Project: Underskinning and other Mods

[DSwatloski]

I'm going to tinker with my Harris (see signature). I has a a 15" X 15" Pitch SS Power Tech cupped prop.

The boat loaded runs 22 MPH by GPS at max 4800 to 4900 RPM measured by a stock analog tachometer. The engine should turn upward of 6000 RPM. RPMs are too low.

When the engine is trimmed up at all it pushes water up between the lower unit on the engine onto the deck. I confirmed with Harris that the boat seller mounted it too low. It's set up for their tritoon performance model. The engine is presently as low as it can go on hole one. (Edit added 4/11 - Now that I can access my boat, I can see the motor was mounted on hole 3 at one time. That's where I'm going to set it.)

Mods I'm making:
1) Under skin the boat stern to bow with 5052 Aluminum, SS Screws probably with neoprene washer, and permatex to keep them from backing out. I will put an 80 degree bend on the outer edges to close the gap between the deck and pontoons. I'll do some performance runs to see the impact on speed if any, GPS of course.
2) Raise the engine to hole three. Might be too high, but I sit very low in the water and I usually have five to seven people on the boat with two ice chests.
3) After some runs with the current prop at hole three, I will decide if the motor needs to go down to hole two. Cavitation and blowing out in turns will be my criteria.
4) If I'm not in the RPM range upper 5000's, I'll look to prop swap.
5) Potential Mod, depending on what I see after step three, I might send the ECU to Simon Motorsports for the tweak to the 115 to 120 HP range.

I'll be posting up pictures and comments as I go forward with this next week or two. I might have some GoPro video boat under the deck underway, before and after the underskinning.

Comments based on your experience are welcomed.

Dave

[Bryden24shp]

I agree with all the above! 25 hp from the ECU upgrade may not give you a lot of a spreed increase. It takes a lot of hp to go faster. But you'll notice better fuel economy, holeshot and a nice mid range punch. All of what you individually mentioned, will help you out. All together will be like driving a new boat. Mostly the underskinning. Lets see pics of the projects as you go. I love tinkering with them, too.

[mzodarg]

Had similar low RPM issues with my 2015 90 hp CT fourstroke merc. I was pushing about 5300 rpms at 26-28 MPH. Now I'm hitting 5600 rpms and top speed is just north of 30 mph (GPS) with a 15x17P aluminum prop. The boat does run better, better hole shot, sips fuel and handles good.

I did try an enertia 15x15 SS prop, the barge would spin at 6000 rpms but my top speed was 26 MPH.

I'm sharing my experience to give you some insight on what to expect. My expectations with Simmon were way higher than my results.

I'm not underskinned and I do have a pontoon, not a tritoon. Your results my be different.

Mike

[DSwatloski]

mzodarg, So you picked up 3 to 5 mph for a $650 donation to Simon Motorsports, plus better fuel consumption?

I will put up the pics as I progress. I hope to be able to put up some MPH stats (GPS based) and pictures as I make the changes. Baseline, skinned, engine raised, repropped and then potentially the Simon Motorsports ECU.

Thanks for the advice Bryden24shp & mzodarg

[Bryden24shp]

You'll want to wait until after the ECU to prop. Your upper RPM limiter will be changed. I'ld hate to see ou spend $ on everything then have to pop for another prop. Been there... Done that.... I have over $1500 in props on Ebay right now that I will never use again.

[DSwatloski]

You'll want to wait until after the ECU to prop. Your upper RPM limiter will be changed. I'ld hate to see ou spend $ on everything then have to pop for another prop. Been there... Done that.... I have over $1500 in props on Ebay right now that I will never use again.

Makes sense, what engine are the props for?

[teecro]

You'll want to wait until after the ECU to prop. Your upper RPM limiter will be changed. I'ld hate to see ou spend $ on everything then have to pop for another prop. Been there... Done that.... I have over $1500 in props on Ebay right now that I will never use again.

Makes sense, what engine are the props for?

Pretty sure for a big Mercury Verado....

[teecro]

DS...

1) Without question hands down do the underskinning as from all the reading that I've done not only will it improve speed a small to sizable degree it will improve overall handling of the boat as you will no longer be taking slap wave action on your crossmembers. I've wanted to get mine done since near day one, but I keep finding other stuff in my way.
2/3) I can't tell you how much to raise your engine but from your details your too low and you know that. I'd suggest only one hole at a time and don't search for too much gold in raising the motor as after all these are pontoons and not planing hulls. Too high and you blow out and/or lose bite in turning.
4/5/6) Max Full Throttle RPM on your motor currently is 5 to 6 grand and you would like to be as close to 6K as practical with a light load. If you get Simon to tweak your ECM you will get some extra speed from 25 to 30 more ponies but your rev limiter is only going to be 6,200 RPM so your not gaining anything but the "ability" to get to max WOT with an increasingly heavier load...
Keep in mind that 3-Blade props are always going to be faster than 4-B but they give up bite and blow out easier... And stainless is almost always going to be faster as they don't flex like an alum prop does....

[DSwatloski]

teecro,

Thanks. So you moved your 75 HP Merc to 115 HP with a Simon Motorsport ECU? Happy with it, I'd guess?

Do you know if the reburn ECU is detectable by a run of the mill Mercury mechanic when they put it on the computer? Or does it look like the original equipment?

Dave

[DSwatloski]

teecro,

Thanks. On the motor move, it is really low, as low as it can go. The factory told me hole 2, I may go to 3 and then move it down top hole 2 if I get cavitation. When I trim other than max down I have a foot bath on the back of the boat. It pushes up water between the lower unit and the transom.

So you moved your 75 HP Merc to 115 HP with a Simon Motorsport ECU? Happy with it, I'd guess?

Do you know if the reburn ECU is detectable by a run of the mill Mercury mechanic when they put it on the computer? Or does it look like the original equipment?

Dave

[teecro]

... So you moved your 75 HP Merc to 115 HP with a Simon Motorsport ECU? Happy with it, I'd guess?

Do you know if the reburn ECU is detectable by a run of the mill Mercury mechanic when they put it on the computer? Or does it look like the original equipment?

My ECU is sitting in the garage while I sit on board ship till next week... I hope to be happy with no sooner than the 10th...

From what I've been told the burn is not detectable in any way other than factory or manf testing.

Also I know exactly what your talking about with the water climbing up your motor. My first motor a 60HP did this too when I removed a troublesome fin under the motor pod that on some Sun Trackers increased blowout. On installing the 75HP we went up one hole from bottom and the problem has never returned. BTW the 60 Big Foot has the same foot casing as the 75 so under water its all the same...

[DSwatloski]

Very Nice. You should have fun with it. I'm going to do mine stages after I do the first oil change this week. I'm gong to: Skin, performance run. Raise motor, performance run. Then decide on the ECU before I reprop.

[teecro]

Very Nice. You should have fun with it. I'm going to do mine stages after I do the first oil change this week. I'm gong to: Skin, performance run. Raise motor, performance run. Then decide on the ECU before I reprop.

Thanks I plan on having fun one with it one way or the other... I'm keeping my fingers crossed that the current 12P stainless prop will perform well as I was right at 5,500 RPM and knocking on 28 MPH so hopefully with the new found ponies it will spin right up to 6K right around 33/34 MPH... I do have an alum 13P to try also...

[mzodarg]

mzodarg, So you picked up 3 to 5 mph for a $650 donation to Simon Motorsports, plus better fuel consumption?

I will put up the pics as I progress. I hope to be able to put up some MPH stats (GPS based) and pictures as I make the changes. Baseline, skinned, engine raised, repropped and then potentially the Simon Motorsports ECU.

Thanks for the advice Bryden24shp & mzodarg

That's correct, all this was done on stock 15x17p aluminum prop. Like I said the whole shot is damned impressive, fuel mileage is vastly improved and I'm still over propped. All my speeds were done on GPS in similar conditions.

I haven't pursued the prop issue as I've already thrown money away on an enertia 15x15 SS prop that produced miserable results and to be honest with I am beginning to realize that it's a pontoon boat.....

Copied from another thread a post shorty after I tested the simmon.

update:

So after having the engine raised one hole I took it out this morning. She spun at a whopping 5300 RPM's 31.4 MPH better, but not what I was hoping for.

It was fricken cold 27 degrees and she would blow out in hard turns. I'll probably lower it back down and chase the prop next

[Bryden24shp]

You'll want to wait until after the ECU to prop. Your upper RPM limiter will be changed. I'ld hate to see ou spend $ on everything then have to pop for another prop. Been there... Done that.... I have over $1500 in props on Ebay right now that I will never use again.

Makes sense, what engine are the props for?

Pretty sure for a big Mercury Verado....

Yep, I could use them on the Yamaha since they use the Flo-Torque hub. But, they are all Lefties. The Yamaha is a righty and it can't be reversed, due to the gearcase thrust bearings. According to Ken at PropGods, the only reversible grearcases on the market is Suzuki outboards and older Bravo One's.
So, that said... Anyone need a leftie Merc prop? I have 4...