Inboard engine, plywood spacers?

Long time lurker, finally joined up and decided to add to the community when I can.

I'm in the process of a near full resto on a 1981 Sportcraft 270. It's an inboard with Merc 225/GM 350 mated to a 72Cr velvet drive.

I've cut off the rear top 3rd of the cap to access the transom, removed all tanks and accessories, and just finished pulling the engine to get ready to cradle, drain, and tub the rest of the boat .

My question is, plywood spacers that are on top of the engine and trans mounting beds... It appears to be two 3/4" plywood chunk 'spacers' in between the engine mounts and the mounting beds. When I rebuild the stringers and engine beds, do I want to keep the engine beds at the same heights and re-utilize plywood spacers? Or, should I make a higher bed up to the height of the engine mounts and do away with the spacers?

I'm just not sure if these spacers are providing some function that's unbeknownst to me (vibration elimination, corrosion preventative, etc?). To me, it seems odd at first thoughts, but I've also never ran across this on the I/O's I normally work on. This is the first full inboard we've owned and am rehabbing.

Here's pictures for clarification of what I'm trying to explain. Don't mind the water, the boat angle on the trailer doesn't sit the front end high enough to drain properly. Once on the cradle, it'll be dried and done properly, hehe.

 

You’ll probably need the height, but I’d rather see something more substantial for a spacer.
I’m surprised those aren’t rotted away, given the standing water!

 

You and me both were surprised! Haha. Once it's up on a cradle, we'll be getting rid of all that nasty water and moisture.

We're putting in new engine beds and stringers. So, should we use a spacer of sorts like they had? OR, should we just build the engine beds taller and eliminate the need for the spacers altogether?

Is there any other purpose for those spacers other than the engine height? Vibration relief, stringer protection from metal sitting directly against glass, or some other reasons?

 

I’d build up the beds , but consider using some hefty aluminum angle long enough to carry both fore and aft mounts.
There’s some good reading available at sbmar.com in the “Tips “ section.

 

Thanks for the tips. I really appreciate it! I agree, using some nice thick aluminum or etc for supporting the mounts, much more reliable than plywood with holes in it, haha.

 

If you're going to replace the stringers (a big task that must be done correctly) take the time to learn stringer engineering and how your engine should be mounted for maximum stability. Back about 10 years ago I did a similar job when restoring a small cruiser.

Before you remove the old stringers take a good look at them and try to determine if they were built in the correct place to begin with. Don't assume that because the boat came out of a factory that the factory did it right. The ply may have been added at a later time to correct for an alignment issue or it may have been done at the factory. I'd guess the later time as it hasn't rotted away.

You may want to make a jig before you remove the old stringers so that you will know where the engine beds will be when you build the new stringers. Once the old stringers are gone you won't know where to place the beds without some kind of guide.

You might want to consider a better mounting arrangement. I think the squared off stringer with the engine plopped on top and lag bolted is the lazy mans way of doing this.

Consider spreading your stringers a bit and using 3/8" aluminum angle. Doing this is a little more work but will allow you to build your stringers a little higher and when done will provide a very stable mounting arrangement. You'll also be able to round off the top of the stringers which is much stronger and it's easier to do a fiberglass layup that way. Glass hates sharp corners.

I'll post a couple of photos below to give you an idea.

The wooden inserts provide compression strength when clamping in new beds.

Notice no sharp corners. There are backing plates on the side of the stringer you can't see.

This more recent photo shows the backing plates. I used aluminum for the shims on the back mounts. No shims on the front mounts.

Dave Gerrs book, "The Elements of Boat Strength" was the resource I used to figure out how to build my stringers.

Good Luck with your project. Do it once, do it right and you'll be glad you did.

MIA

 

Thank you so much! That really gives me a good perspective on the mounting perspective. This will be my 4th boat resto, but this is the biggest one I've done, as the last one was a Sportcraft 250 and a couple Wellcraft 210's before that.

I figured if we do this right and do it once, we'll have a forever boat and be happy we finally "made it". As this is the boat we've wanted for many years here on Lake Erie, but just haven't came across any.

I see what you mean about checking the stringer placement, because it seems like most everything on these boats were slapped together by half drunk monkeys... So I'll definitely be on the ball with measurements and placement.

I really like the way you mounted the engine. I had the thought that I wanted to go with something like that, that bolts THRU the stringer and spreads out the load rather than the common "plop on top with a couple lags" type way. It just seems like a recipe for eventual disaster doing it the lag screw way.

I thought about doing an offshore type mounting bracket, but they're completely solid/rigid, and I'm just wondering if that will pose vibration issues through the hull and stringers, so I really like your way of doing it, as I see you have the double cushion brackets on the rear.

Making a JIG for the engine placement is an EXCELLENT tip. Much better than what I was going to do (mark and measure from a few different locations all converging at the specific mounting points). A JIG will solve ALL of that mess, but without the headaches.

I've learned a TON about stringers, fab methods, materials, and everything else I can consume on the subject over the past 6yrs or so. So, I'm hoping I can begin to start putting it all to use here shortly, and eventually reap the benefits of the pain, stress, and labor that's going to inevitably go into it.

The plan is new stringers, new transom, and new sole with a new engine and rebuild/refresh the Velvet Drive... Then, eventually later on down the road do the top half of the boat from the sole on up. So, I plan to be on here with many more questions, inquiries, and problems that I will inevitably run into (as well as help others with the things I'm really knowledgeable in such as gas inboard engines and Volvo outdrives, etc).

Thank you so much for taking the time to respond with such an in-depth and well detailed response! It is greatly appreciated.