Off-Center Mounting of Outboard

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
alan-bc
Posts: 9
Joined: Tue Jun 29, 2021 7:13 pm

Off-Center Mounting of Outboard

Postby alan-bc » Thu Jun 23, 2022 1:21 pm

Q1: on a SPORT 15 Is mounting an outboard engine off-center a normal installation?

Q2: is a list to Starboard at rest normal for a SPORT 15 hull?

BACKSTORY: The outboard on my SPORT 15 I bought in Summer 2021 is mounted off center by 1/2-inch. The lower [Port] hole is 27-inches from the [Port] gunwale; the lower [Starboard] hole is 26-inches from the [Starboard] gunwale.

Sitting at the dock, the boat has always [had a list to Starboard]. I always thought [the cause of the list to Starboard] was the weight of the console"and battery on the [Starboard] side, but I see now that the [off-center engine] mount contributes to the list.

[To correct the off-center engine mounting] will be VERY tricky--if even possible. New 1/2-inch-diameter holes will have to be drilled about 1/2-inch away from the existing 1/2-inch holes--and that might not go wellI.

I'm giving serious consideration to moving the console to the [Port] side of the boat, but doing so would require modifying the steering, the throttle will look goofy and so forth.

It's my first powerboat. I have been a sailor all my life before this.

Give me your thoughts [on moving the console to the Port side of the boat and on drilling new holes and on the effect of the engine being 1/2-inch off center]

Alan

dtmackey
Posts: 701
Joined: Thu Sep 28, 2017 9:29 pm

Re: Outboard off center: normal?

Postby dtmackey » Thu Jun 23, 2022 1:33 pm

The simple answer is NO. Off center mounting sounds like an error when the boat was powered. It should be on the centerline of the boat.

D-

jimh
Posts: 10370
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Off-Center Mounting of Outboard

Postby jimh » Thu Jun 23, 2022 3:08 pm

I would leave the engine mounted as is. I doubt that the 1/2-inch offset is affecting the propulsion of the boat or the static trim.

I would leave the helm console where it is now.

If you decide to re-do all the engine mounting holes, read the FAQ answers related to that work.

Q8: How Does the Engine Mount to the Transom?
https://continuouswave.com/whaler/reference/FAQ/#Q8

Q9: What is the Standard Transom Hole Layout?
https://continuouswave.com/whaler/reference/FAQ/#Q9

The c.1976 SPORT 15 has a shallow engine splash well. Read this article:

Transom Mounting Hole Layout for Shallow Splash Well
https://continuouswave.com/forum/viewto ... f=7&t=5808

If you become obsessed with the engine mounting height, read this article

Considerations in Engine Mounting Height
https://continuouswave.com/forum/viewto ... f=7&t=6618

A POSSIBLE SIMPLER REMEDY
If you discover that the SPORT 15 with engine 1/2-inch off-center exhibits some awful tendency to steer to Port, you may be able to correct for that with adjustment of the engine trim tab on the bottom of the Anti-Ventilation plate. See the owner's manual for advice.

If you do not have a printed copy of the owner's manual, I have reproduced the owner's manual in HTML. See

Owner's Manual 9 to 17-foot Hulls
Table of Contents

https://continuouswave.com/whaler/reference/manual9-17/

TRIM TAB ADJUSTMENT
https://continuouswave.com/whaler/refer ... ml#trimTab

ASIDE: as a sailboater, you might recall a rather common practice on some sailboats with auxiliary inboard engine power: the propeller shaft was not mounted precisely on keel center line, but instead was angled slightly to port to compensate for the tendency for propeller torque to propeller torque to walk the hull to port or a right-hand propeller.

I used to cruise a 30-foot sailboat with a propeller shaft on centerline and also angled downward. We spent a lot of time sailing actually being underway under engine power--the little secret of sailing. When under power the boat would never track true to straight ahead; it always crabbed to port. Anytime we anticipated holding a particular heading for along time we always added 5-degrees to the course to be steered to compensate for the propeller torque.

alan-bc
Posts: 9
Joined: Tue Jun 29, 2021 7:13 pm

Re: Off-Center Mounting of Outboard

Postby alan-bc » Thu Jun 23, 2022 11:18 pm

Thanks to all who replied.