GLS 13 60-HP

Optimizing the performance of Boston Whaler boats
Aquaman
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GLS 13 60-HP

Postby Aquaman » Fri Jul 24, 2020 1:26 am

I have 1999 GLS 13. An almost new 2004 Mercury 60-HP FOURSTROKE engine is mounted with the anti-ventilation plate two inches higher than the keel. The boat drives well and turns without propeller venting.

The total boat weigh in about 900-lbs by my calculations.

Engine speed at full throttle is only 4,300-RPM, and that is with only me on board.

I don't have a speedometer, but my friend’s boat paced me and estimated boat speed as in the low 30-MPH range.

The propeller is a 10-1/2 x 15 four-blade TROPHY SPORT with what appears to be heavy cupping. My dad had it shaped and he calls it a surface piercing prop. The engine and propeller were on a high speed DUX inflatable before.

I don't know the lower drive gear ratio.

The engine has [an added A-V plate foil appendage [that I call] a “whale tail.”

The boat is smooth and will plane with six people and added gear, but it feels kinda gutless on the low end.

[Is the propeller pitch too high]?

The WOT engine speed range is supposed to be 5500 to 6000-RPM.

The throttle is hitting the stop by the linkage so I think I'm getting full throttle.

I feel like this motor should be able to spin that propeller easily.

Am I wrong?

All the research I have done has found most people are running same diameter but 13-pitch for that engine on bass boats—the closest example I could find to a small skiff and a Mercury. 60-HP

[Readers: give me] ideas [to increase the engine speed at full throttle to be in the recommended range].

[Can you give me those ideas] before I start throwing money at new propellers or engine techs?

Can the propeller I have now be re-pitched?

I am happy with the boat as is but would like to get full performance out of the engine. My goal is to be able to pull my 120-lbs kid on a wake board. I have clocked many hours in older whaler 13-foot boats with 40-HP two-stroke-power-cycle engines and 25-HP four-stroke-power-cycle engines. I know that it can be done.

I also know the 13GLS hull is different, and that a lot of weight is being carried.

Thanks for your consideration of my dilemma.

biggiefl
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Re: GLS 13 60-HP

Postby biggiefl » Fri Jul 24, 2020 9:36 am

The boat and motor should weigh around 600lbs.

You can not repitch a prop to gain 1200-1700rpms.

Are you sure the tach is correct?

Even going to a 12" would only bring you up around 600rpms.

Something is not correct and you should be doing 40+ even with some gear.

Now if it is doing 4300 with 6 people in it, that is another story and you need a larger boat.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

jimh
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Re: GLS 13 60-HP

Postby jimh » Fri Jul 24, 2020 10:09 am

No serious propeller testing can be done without a measurement of boat speed.

Aquaman
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Re: GLS 13 60-HP

Postby Aquaman » Fri Jul 24, 2020 11:09 am

Thanks for the replies.
The tachometer is a good one but one thing I didn't think of is the original motor was a 3cyl. The 60 hp is a four. Is the signal the same or do I need a tach for a 4cyl?
RPMs at idle seem accurate. I agree, that i need my own speed measuring device and am researching that as a gauge. I guess I was mostly concerned with the RPMs being so low and the speed being relatively slow for what seems like a large hp motor. Also my holeshot is seemingly weak. I'm comparing it to an older whaler with a 2 stroke40 that was way lighter, and well, a 2 stroke.
My weight by spec:
Hull 320lbs
Motor 257lbs
2 batteries 90lbs
10gallons fuel 80lbs
Anchor, swim step, Bimini 60lbs
It's well distributed but yes it's a lot.
I did shuttle close to 1000lbs of humans with additional ice chests and 2 paddle boards for a five mile trek.....amazing little boat.

Aquaman
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Re: GLS 13 60-HP

Postby Aquaman » Fri Jul 24, 2020 11:11 am

Is the spooning on the prop something I should be concerned with?

biggiefl
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Re: GLS 13 60-HP

Postby biggiefl » Fri Jul 24, 2020 12:12 pm

Pull the tach and see if it has pole settings, you will need to change that to a 4cyl. If not switchable, you probably need a new tach. Also the tach for newer engines usually has warning lights and other diagnostic stuff built into it. If this tach is older than 15yrs or so, it needs to be upgraded to the newer mercury system which is a couple hundred bucks.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

biggiefl
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Re: GLS 13 60-HP

Postby biggiefl » Fri Jul 24, 2020 12:12 pm

How far out are you trimming it? Have you tried it w/o the fin on the plate?
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

jimh
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Re: GLS 13 60-HP

Postby jimh » Fri Jul 24, 2020 12:18 pm

Tachometers are not universal, that is, they only work accurately with the specified engine they were intended for use. Some tachometer have adjustments to obtain accurate calibration with signals of different engines.

Older two-stroke-power-cycle outboard engines with permanent magnet alternators use a half wave rectifier tap as the source of the tachometer signal. The signal varies with the number of alternator windings or “poles” in the alternator stator.

The tachometer reading you are getting for the Mercury FOURSTROKE on your old tachometer is very likely way off.

For any serious propeller testing the engine speed must be measured very accurately.

Invest in modern engine instruments.

jimh
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Re: GLS 13 60-HP

Postby jimh » Fri Jul 24, 2020 12:25 pm

Small four-stroke-power-cycle outboard engine are known for their narrow engine speed bands where the engine develops maximum torque. To describe a four-stroke-power-cycle engine as “gutless”—which may be a way to say lacks low engine speed torque and cannot accelerate rapidly under load—would be typical. Those engines generally only develop their rated horsepower over a narrow range of engine speeds and usually only in the very upper end of their allowed engine speed range.

These deficiencies are over come by superchaging, very large displacement, variable valve timing, tuned intake manifolds, and other enhancements which add weight, complexity, and cost, and none of them will be found in a 2004 60-HP Mercury FOURSTROKE.

jimh
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Re: GLS 13 60-HP

Postby jimh » Fri Jul 24, 2020 12:35 pm

Most modern smartphones can display speed over ground from GNSS satellites.

As the boat being discussed in this topic is running now, we have no good data for boat speed, engine speed, and engine gear ratio.

There really is no reasonable way to assess performance of the boat since we really do not know how it performs.

Aquaman
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Re: GLS 13 60-HP

Postby Aquaman » Fri Jul 24, 2020 5:47 pm

You're very right on all accounts. It's possible I am getting full motor RPMs and my tach is off. The tach is fairly new but I'm not sure of the calibration on 3vs 4 cyl.
I do know that I'm not topping 35 mph as a very accurately gauged ski boat walked away from me at that speed. I'll work on finding a dash speedo and checking the accuracy of the tach. I may also pick up a 10.5x13 aluminum 3 blade just to try it out as they aren't too pricey. I have to say, I am very partial to stainless props even if it is potentially the wrong one.
I am enjoying this boat. It feels a lot more refined than the early model classic 13s.
Thee extra freeboard alone makes this engine experimenting an option.
Thanks for the replies and I'll repost when I have more detailed info.
Where do I look for the lower unit gear ratio? Is there a marking somewhere?

biggiefl
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Re: GLS 13 60-HP

Postby biggiefl » Mon Jul 27, 2020 1:43 pm

Can you post a pic of the boat & engine?
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

jimh
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Re: GLS 13 60-HP

Postby jimh » Mon Jul 27, 2020 11:10 pm

Most smartphones have a GNSS receiver and can display speed over ground. Or a laptop can work with a GNSS receiver (about $35) with a USB interface to see speed over ground.

Engine gear ratio is usually given in the specifications section in the owner’s manual.

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Phil T
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Re: GLS 13 60-HP

Postby Phil T » Tue Jul 28, 2020 11:41 am

A 2004 any make/model is not "almost new".

With the prop modifications, we have no idea what the pitch of the current prop. Prior to 2002 the selling dealer rigged the engine and selected the prop.

It is clear that the current prop has too much pitch for the hull.

Note that Trophy Plus props are only recommended for 75-115hp engines. The smallest pitch offered is 17".

Reviewing Whaler's drawings/diagrams it is worthwhile to note that the 2003 150 Sport with the Mercury 60hp FourStroke motor was equipped with the 13-3/8 x 14 SST prop. This model is heavier than yours.

In using a commercial prop calculator, we input WOT RPM of that model which is 6,000, gear ratio of 1.83 for FourStroke (2.33 for Bigfoot models) target speed of 38mph, prop slip of 5% and it calculates a pitch of 12.

I would start with the 13-3/8x12 SST and go from there.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

biggiefl
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Re: GLS 13 60-HP

Postby biggiefl » Tue Jul 28, 2020 12:19 pm

Is this a bigfoot or little foot gearcase?

Did'nt the 150 come with the bigfoot only?
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

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Phil T
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Re: GLS 13 60-HP

Postby Phil T » Tue Jul 28, 2020 12:57 pm

Nick - IDK.

If the OP has a Bigfoot model, the prop calculator returns 16" of pitch.
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003