Motor Stringer Width Spacing?

Designs for inboard or outboard power

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Motor Stringer Width Spacing?

Post by garrys »

I'm at the point in my Monaco build where I need to attach my motor stringers to my building form. The "instructions" say 26 inches apart. Is that inside to inside, or center to center, or outside to outside? My motor stringers are 1 13/16 in thickness.

The instructions also say to attach the motor stringers to the transom vertical uprights. The transom vertical uprights (built to plans) measure 26 1/2 outside to outside, and 24 3/4 inside to inside. The engine I plan to use is an Indmar or PCM small block Chevy.

My dilemma is that if I mount the stringers to the outside of the transom vertical uprights, then my overall (outside to outside) width of the stringers becomes slightly over 30 inches.........which is wider than the space between the frames at the floor timber gussett. Confusing?

Garry Stout
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Post by lakeracer69 »

At bare minimum you will need 24" INSIDE TO INSIDE measurement between the motor stringers. Look at the measurements for your building form, a clue may be found there. Look at front and rear motor mounts, they need a minimum of 24" to fit as well as the center support bearing mount.
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Rich Coey
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Post by Rich Coey »


The verticals on your transom should have been 26" outside to outside with the stringers mounted on the outside giving you 26" between stringers and 29" outside to outside. Your verticals spaced 1/2" wide and the stringers 1 13/16" instead of 1 1/2" is causing the problem. You could redo the verticals on the transom to get the 29" outside on the stringers or notch the stringers at the intersection with the transom to get what you need.I think the notch would work fine with the extra thickness you have on the stringers .


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Post by kens »

You may want to account for the width of your motor beds when figuring the inside dimentions of stringers.
I would look at the installation drawings of the motor you want to use, and notice that those motor mounts are on approx. 24" centers; they in turn mount to the beds; which generally mount inside the stringers.
The install drawing for your motor will give you a tolerance of the motor mount width (usually 22-24 inches) on centers.
As a example, my motor mounts were set at 23" centers, plus the beds (3" angle iron) = 26" inside of the stringers.

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Post by BruceDow »

Ken nailed it.

FWIW, I am using a ChrisCraft SBC engine. I had the engine before I set the building form and put those verticals in the transom. I knew that those transom verticals set the witdth of the stringers, so spent a lot of time measuring to make sure I had enough clearance.

I think the 26" reference is centre-centre.

The inside-inside measure is the critical one. If you are too wide, you can use stouter engine beds. If you are too narrow, you are toast.

My measure is 24-1/2" (inside to inside). that would make my outside measure about 28-1/2". I would have had no problems with my engine installation if they were an inch or so wider. Assuming your engine is like mine, you should be fine with 30" O-O/26" I-I. I like Rich's idea of notching the back of the stringers slightly if you think they are too wide.

I do recall having to notch one of the frames (#5?, #6?) toward the bow to "accept" the stringers. (I think this might have been noted on the plans or patterns somewhere.)

Good luck.

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Dwain the ski king
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Post by Dwain the ski king »

I might add my 2 cents worth....I have the same engine as Bruce(185hp CC Chevy, flywheel-forward) AND, I could have used a little room between the stringers(mine are 24" inside) just for room to remove the starter or fuel pump to work on them...Also, my water pump is underneath the motor(mainfolds), and is hard to access for repairs. You can always make the motor mounts wider to accommodate the width of the stringers...I recommend at least 26-28"inside.....Dwain, the Ski King...

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