16 SL with HONDA BF90

Optimizing the performance of Boston Whaler boats
cbards
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16 SL with HONDA BF90

Postby cbards » Tue Jul 23, 2019 8:20 am

A 1993 SL16 has a 1997 Honda BF 90 mounted all the way up, and a 13.5 x 15 Honda aluminum propeller.
Engine speed = 6300-RPM WOT
Boat speed = 33 MPH

Give a recommendation on propeller upgrade.

The 16SL now has significant bow rise and porpoising.

biggiefl
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Re: 16 SL and Prop

Postby biggiefl » Tue Jul 23, 2019 10:50 am

[A 16 SL was] Not really designed for that [HONDA engine]!weight so that might heighten the porpoising.

Q1: Can any weight be moved forward like battery?

I would probably get same size propeller but SS which may drop engine speed 100-RPM or so—no biggie.

Seems like a small propeller for a 16-foot boat and 90-HP.

Q2: What is WOT range?
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

cbards
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Re: 16 SL and Prop

Postby cbards » Tue Jul 23, 2019 3:56 pm

1997 Honda BF90 WOT range is 5000-6000 RPM with a 2.33 gear ratio. leaning towards SS 13.25 x 17 prop

jimh
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Re: 16 SL with HONDA BF90

Postby jimh » Wed Jul 24, 2019 10:12 am

I don’t think a remedy for excessive bow rise while transitioning to plane and oscillating bow while on plane will be obtained by a propeller change.

Reduce weight in the stern.

What is the engine mounting height as described by the number of holes above lowest position?

biggiefl
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Re: 16 SL with HONDA BF90

Postby biggiefl » Wed Jul 24, 2019 10:29 am

He just raised the engine mounting, but now the engine speed is exceeding the redline. A 17-pitch should get the engine close to 6,000-RPM.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

flymo
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Re: 16 SL with HONDA BF90

Postby flymo » Thu Jul 25, 2019 7:01 am

[The HONDA BF90 engine is] hitting the rev-limiter at 6300 RPM, so to tell what pitch you should be at is hard with that data.

I recommend a quality stainless steel propeller with a stern-lifting design to reduce the porpoising.

Try a PowerTech SCD-3 in a 18-pitch.

You may want to connect with ken@propgods.com. He sells PowerTech (at the best price I have found) and is a good source of specific recommendations.

cbards
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Re: 16 SL with HONDA BF90

Postby cbards » Wed Aug 21, 2019 2:57 pm

Update; After working with Prop Gods I installed a Power Tech SCD3 17-pitch stainless steel propeller.

Now has faster acceleration onto plane from a standing start.

[Engine speed was] 6000-RPM trimmed in. And boat speed increased by trimming out before having to slow down.

Still experiencing some bow rise.

Winter projects will be:

—relocate battery to the port console
—remove the many years of flaky old bottom paint and ——sand gellcoat to shiny.

Thanks for all the advice.

cbards
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Re: 16 SL with HONDA BF90

Postby cbards » Tue Jul 28, 2020 3:57 pm

For the 2020 season i have been able to get the battery relocated to the helm position.

I installed a Power Tech SCD3 17-pitch stainless steel propeller last year.

The fuel tank capacity has been reduced to 17-gallons, and the fuel tank has been pushed forward in the fuel tank cavity.

With a personnel load of roughly 500-lbs, the HONDA 90 engine accelerates to its redline at 6300-RPM. Boat speed-over-ground is then 36-MPH measured by a GPS receiver.

With fewer people on board and with the HONDA 90 engine trimmed all the way out, engine speeds exceeds redline and accelerates to 6600-RPM: boat speed over ground is then 39 to 40-MPH per GPS.

The 16 SL still exhibits some bow rise [during transition to plane].

Should I increase the SCD3 propeller pitch to 18-pitch from 17-pitch in order to lower engine RPM?

Would a four blade propeller help reduce bow rise?

How much top end speed is lost with four blade?

Boat weight is about 1025-lbs; engine about 360-lbs

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Phil T
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Re: 16 SL with HONDA BF90

Postby Phil T » Tue Jul 28, 2020 7:26 pm

You definately want to move up two-inches in pitch with the same make and model of propeller . If you change propeller models the pitch sizes are not applicable.

To control bow rise, the one feature that will help is smart tabs. Read "Thegage"'s post, 2nd to last on this thread:

http://continuouswave.com/ubb/Forum3/HTML/020941.html
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

Saukit
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Re: 16 SL with HONDA BF90

Postby Saukit » Wed Jul 29, 2020 2:42 am

I have a 1992 16SL which unfortunately has been plagued with fuel problems resulting in not a lot of time in the water. But I have done a few things which may provide a data point or two.

My 16SL has a 2006 Mercury 90-HP EFI engine, and the battery is under the port rear seat.

The propeller was a three-blade stainless, which, despite pulling off the boat and looking all over, has no identifying marks that I can find. I would guess it may have been a standard 16 or 17-pitch propeller,

I bought the 16 SL with a Doel-Fin on it, and the boat was flat out scary over 35-MPH, or so. The 16SL wandered all over the place. I pulled off the Doel-Fin—at the launch ramp and put the boat back in.

The 16SL was now much more stable, but getting on and staying on plane was terrible. The 16 SL was stern heavy, and in chop the 16 SL had to go 20-MPH to stay on plane—a brutal tide. This was not so fun in a 16-foot boat on Lake Washington.

My next steps I wish I had performed in sequence with testing between instead of both at the same time—but hindsight and all.

I rented an engine hoist and my buddy helped me raise the Mercury 90-HP engine as high as it would go, three-holes-up I think it's called.

At the same time, we installed a Solas HR Titan four-blade stainless 13.25 x15-pitch propeller. My research on this propeller indicated it was a stern-lifting propeller designed to permit a boat to plane at low speeds. This was important to me because I want to be able to make some progress in chop without beating the crap out of my passengers.

Sadly, this is the point in my tinkering where mechanical problems have prevented me from doing a lot of testing. The few times I've had the 16 SL out make me think that the four-blade stern lifter is just what this boat needs. It planes way faster and holds plane in rough water at much slower speeds. But by the time I got a new GPS rigged and was getting ready to test top speeds, I ran into my fuel problems. The first time I took out the 16 SL to check boat speed and engine speed, the Mercury 90 engine died; it hasn't run right since.

I let the 16 SL sit too long. The boat has been at the shop recently in the hope we can get the Mercury 90 engine running again.

I think I might want another degree or two on the propeller.

I definitely think this 16 SL wants the engine mounting height to be high [three-holes-up], and the propeller to be a four-blade and also a stern-lifting type.

jimh
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Re: 16 SL with HONDA BF90

Postby jimh » Wed Jul 29, 2020 7:52 am

Some Mercury engines have five sets of mounting holes, which can allow the engine mounting height to be as high as four-holes-up from lowest position.

The propeller test described above compared an unknown brand and model and pitch three-bladed propeller against a particular stainless steel four-bladed propeller, and the engine mounting height was also changed. I don’t think the conclusion that a four-bladed propeller must be the best choice can be justified from this one test.

The improvement in boat performance could be attributed to any of the changes:
—raised mounting height of engine
—change in propeller pitch or rake or diameter or cup or any element of the design other than number of blades


For more discussion on three-bladed and four-bladed propeller comparison testing see

viewtopic.php?f=7&t=5172&p=29660

Also follow hyperlinks in the linked article to two more good discussions on this topic.

jimh
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Re: 16 SL with HONDA BF90

Postby jimh » Wed Jul 29, 2020 9:04 am

Saukit wrote:I think I might want another degree or two on the propeller.


The only dimension on a propeller measured in degrees is probably blade rake. I think you were talking about rated pitch, measured in inches.

Saukit
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Re: 16 SL with HONDA BF90

Postby Saukit » Wed Jul 29, 2020 8:43 pm

jimh wrote:
Saukit wrote:I think I might want another degree or two on the propeller.


The only dimension on a propeller measured in degrees is probably blade rake. I think you were talking about rated pitch, measured in inches.


Thanks for the correction, yes I meant another inch or two of pitch, not degrees.

I am also in agreement that raising the motor and changing the prop at the same time make it impossible to determine which variable is more impactful on the handling of the 16SL. If I can ever get it running reliably I’ll probably throw the original prop back on to isolate the effect of raising the motor.