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1993 16SL (1997 Honda bf 90)is listing at speed with balanced load and exhibits bow up behavior and some porposing. I will be removing the hydrofoil to reduce the listing. Gas tank was replaced with 17 gallon and pushed forward in the below deck cavity. 1 battery starboard side rear. The motor is mounted one hole up. Original aluminum Honda prop. WOT 6,000 RPM, 30 MPH. I have two questions.

1. What is the ideal mounting height for this motor?
2. What is the ideal prop for this setup?

I would like to address these two issues before considering smart tabs.

Really enjoy this boat and would like to have it run with more stability.

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Craig -

Thanks for your detailed post. So many omit the tech details.

The porpoising is one of the signs the engine is mounted too low. The foil is a bandaid. Take it off.

You realize of course there is no such thing as a standard prop. Engines and props are sold separately. A dealer selected that prop.

What prop do you have installed now? I would suggest, based on your performance, you are under propped since you are only getting 30 mph @ WOT rpm.

I made a list of the engine/props that Boston Whaler owners tested on their boats over the years. For a Honda 90 and a 16' hull, I show:

13.25 x 15 Solas SS
13.25 x 17 Solas aluminum
13.25 x 17 Turbo 1, Yamaha Performance Series.

The engine should be mounted 2 holes up.

How does this read to you?

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Current prop is 13.5x 15 aluminum. Anti Ventilation plate is measuring 3/4 inch below the keel. How high above the keel should it be set to?

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Any idea on make/model or prop part number?

The anti-cavitation plate should be 1-2" above the bottom of the keel depending on the prop selected.

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It is a Honda prop.

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Hydrofoil removed and homes plugged.
I plan on updating my prop to stainless not sure which one yet. Likely 13.25 x17 SS. What motor height does that prop like?

Still trying to figure what bolt height for current prop for this weekends run.

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Through research and measuring I have come to the conclusion that the motor needs to be raised to the three holes up position from the current setting of one hole up. This would move my AV plate from 3/4 below the keel to 3/4 above the keel and max height without drilling.

I will run with current aluminum Honda prop 13.5 x 15 until i can find the correct replacement, hopefully the stock prop performs well with the new running height.

Need to do more research with prop selection. So far i am leaning towards
SS 13.25 x 17 stiletto advantage or similar SS 13.25 x 17.

Any feedback from prop experts is greatly appreciated.

This site contains so much technical information, very helpful.

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You almost can’t get the motor too high on the 16SL. It is stern heavy, and even moving the gas tank forward won’t totally cure that. I ran an E-TEC 90 all the way up, which had the AV plate just below the water’s surface at WOT. I experimented with a number of props, eventually settling on a Stiletto SS, but I can’t remember if it was a 15 or 17, but it’s all about achieving optimum WOT rpm. I did try a four-blade prop, and while it did cure any porpoising it was difficult to get optimum trim. I found that the best setup was the Stiletto prop and Smart Tabs at their lowest setting. The boat popped up onto plane, ran straighter at low speed, but still hit 40 mph on a good day.

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As John has this model, take his advice to the bank. I think he would be running a 13.25 x 17 Stilletto Advantage prop on his E-TEC.

As for prop, you don't want a prop with vent holes. The vents are designed to allow the engine(s) to reach higher rpms in a shorter amount of time, eg large, heavy boats. This is not applicable to your hull.

I would raise the engine and re-test with your current prop noting WOT rpm's and speed before changing props.

Note- The Stilletto line is no longer available hence the list above.

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Guys thanks for the advice. John if you are ever boating in the North Shore MA area let me know, seeing two SL16's together would be a rare sight.

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The boat’s been in Marblehead a few times (where I grew up, and my mother still lives there), and last I knew there was one on a mooring in Little Harbor, just off of Brown’s Island (yeah, I know it’s now called Crowninshield, it that’s not really its name), but I never saw it out on the water. Unfortunately you won’t meet me with my 16SL as I recently sold it. Kids grew up and lost interest, so where it used to sit in the barn is now a motorcycle. It was a great boat, for our family of four.

John K

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John: Congratulations on the sale of your 16SL. You did a very nice job on it with the fine-tuning and detail work. I hope you enjoy your motorcycle riding around Western MA hilltowns.

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After running some tests this weekend with the motor mounted all the way up and the hydrofoil removed (ventilation plate holes patched with epoxy) i have the following results.
WOT 6300 RPM (increase from 6000)
33 MPH (Increase from 30)
Bow rise was significant until on plane, porposing was more noticeable. Great improvement on handling as the boat does not list at speed and comes back to center on turns. I was unable to view the AV plate at WOT to determine if it was at waters surface. Will try that next weekend.

Regarding a prop upgrade 13.25 x 17 Turbo 1, Yamaha Performance Series is the decision i need to make, how will that impact performance?

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You are at/above WOT for the motor. This means your prop has not enough pitch. An analogy is you are pedalling a bike in 2nd gear as fast as you can. If you go up a gear, your pedal speed will drop and speed will increase.

I would price shop the Turbo vs Yamaha (they are the same prop). I would forecast you will pick up 5 mph and WOT will drop to 5900 rpm's.

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Once you get the prop/rpm match right, SmartTabs will address bow rise and porpoising, at the expense of maybe 1-2 mph top speed.

John K

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Update, After working with Prop Gods I installed The power tech SCD3 17pitch SS prop. Now running quicker to plane and better hole shot. 6000 RPMS trimmed in and increasing to mph trimming out before having to slow down. Still experiencing some bow rise. Winter project to relocate battery to the port console and remove the many years of flaky old bottom paint and sand gellcoat to shiny.

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After much testing, 300 pounds of passenger weight on board i am over revving to 6600RPM 40MPH. With 500 pounds of passenger weight I am around 6300rmp 38 MPH.

Not ready to add trim tabs yet as i feel there is still more to discover with props. I am considering a 4 blade to help with bow rise and lower planing speed. Bow rise and low planing speed are a much more common occurrence than being trimmed out at WOT for top speed.

How much top speed is lost with a 4 blade prop?

Any similar hull owners with 4 blade props that can share experiences?