For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL with DF90

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Tony
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For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL with DF90

Postby Tony » Thu Dec 03, 2020 12:07 pm

[For any reader, who, based on their personal experience with Bennett SLT trim tabs on a 17 SSL with a DF90:] what are the benefits of the 6-inch-size tab instead of the 10-inch-size tab?

BACKSTORY: I have re-powered [a 1989 17 SSL boat] with a [Suzuki] DF90. [The new engine does not have a] hydrofoil [appendage added to the engine's anti-ventilation plate]. [There is a] great tendency [for the bow of the 17 SSL to oscillate up and down]. In my mind there is no way to change the weight distribution on the 17 SSL. I may install trim tabs, specifically Bennett SLT tabs.

[Moderator's note: the original question was presented as a survey asking if such a person who met the criteria existed, that is, "Is there anyone...." The forum generally prefers inquires that seek advice, rather than inquiries that propose surveys.}

jimh
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Re: For Readers Who Have Installed Bennett SLT 6-inch Trim Tabs On a 17 SSL with DF90

Postby jimh » Thu Dec 03, 2020 1:02 pm

TONY--you might get more replies if you asked a more general question seeking advice. I suggest a more answerable question would be:

What is a recommended size for a trim tab on a 17-foot hull, specifically a 17 SSL?

biggiefl
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Re: For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL with DF90

Postby biggiefl » Thu Dec 03, 2020 2:06 pm

A 6-inch [trim tab size] will be plenty.

How high is the engine mounted?

What hole is the top bolt in from the bottom hole?

The reason I ask: Suzuki engines like to be mounted high. A low-mounted engne will have the tendency to porpoise more than if mounted higher.

I have had heavier engines than yours on classic 17'-footers, and I never had a [bow oscillation] problem—much less know anyone with tabs on a 16/17 classic.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

Tony
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Re: For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL with DF90

Postby Tony » Thu Dec 03, 2020 2:43 pm

Thanks for replies.

My [17 SSL] has a CMC hydraulic jack plate and the engine is mounted two-holes-up. This gives a 4-inch setback.

The 17 SSL models have the battery, the fuel tank, and bench seat near the transom. They are tail heavy, unlike a Montauk.

The propeller is a stainless steel three-blade from a shop in Louisiana. I couldn’t read a pitch or size in the laser etched hub.

I would hate to put a foil on the new Suzuki engine.

The 17 SSL has a serious problem with bow oscillation.

I haven’t increased engine speed above 3,500-RPM due to break-in guidelines.

With two normal-size guys on the aft bench, [the 17 SSL] bow wants to oscillate.

The boat is kept a lake whose location is a two-hour drive from my location.

biggiefl
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Re: For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL with DF90

Postby biggiefl » Thu Dec 03, 2020 2:50 pm

Wait until you break it in. Might just be a weird speed at 3500 and goes away at 3700.
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: For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL with DF90

Postby Phil T » Thu Dec 03, 2020 3:38 pm

Before you spend $1,000 on trim tabs: bow oscillation occurs due to stern weight and a light bow. The common recommendation for Boston Whaler owners is to review and alter the engine height, select the appropriate propeller, and locate interior items of weight like the battery and fuel tank(s) in a way to lighten the stern weight bias.

On a few select models, trim tabs are still recommended after the above items are complete. The 17 SSL is not a model that needs trim tabs.


With 4-inch setback, the engine height reads to be lower than recommended. I would raise it on the bracket by one hole to start. Once you have completed the manufacturer's recommended break in procedure, test the boat with this single change and observe how it handles. Note - Raising the engine will increase WOT engine speed by 150 to 200-RPM. Take note if you exceed the WOT rpm range of 6300-RPM

A good stainless steel prop is recommended.

Shifting the fuel tank to under a forward seat is a good way to offset the additional weight of a four stroke engine. Owners often increase the space under the seat by relocating the bench to above the side risers. Moeller offers a 13/15 gallon low profile tank that many owners install.
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1992 Outrage 17, 1992 Evinrude 115

Tony
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Re: For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL with DF90

Postby Tony » Thu Dec 03, 2020 4:18 pm

Does the setback of the plate increase bow oscillation at any given height?

Do propellers alter bow oscillation very much?

[The propeller on the Suzuki DF90 on the 17 SSL appears to me to be] a very good three-bladed propeller with cup.

I will review options [for changing weight distribution] and changing the engine mounting height on the jack plate. In the future I will look at fuel tank relocation. [Fuel tank relocation will cause loss of] some very limited storage.

The 17 SSL model is all-fiberglass seating and consoles.

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Phil T
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Re: For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL

Postby Phil T » Thu Dec 03, 2020 4:59 pm

Shifting the engine weight back by using a setback bracket induces bow oscillation.
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1992 Outrage 17, 1992 Evinrude 115

jimh
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Re: For Readers Who Have Installed Bennett SLT Trim Tabs on a 17 SSL with DF90

Postby jimh » Sat Dec 05, 2020 7:36 am

See the topic "Bow Oscillation" in the PERFORMANCE forum for advice on reducing bow oscillation.