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By Rob Rohde-Szudy - Madison, Wisconsin - USA


Motor Well Modifications – Part 4
Finishing the New Motor Well
for the Bolger Light Schooner
…or other boats with similar motor wells

Part1 - Part2 - Part3 - Part4

Last time got though most of the new framing on the light schooner’s new motor well rebuild. Now we’ll finish her up.

Here’s where we left off: (click images for larger views)

Slop Well

We talked a little about slop wells in the first installment, but let’s review. A Michalak-type slop well adds great stiffness with little added weight, gains back some lost sealed buoyancy, adds storage compartments, and helps water and spilled fuel drain more gracefully from the motor well. You can’t beat that. Here’s what it looks like on an AF4B.

The slop well is simply a panel connecting the motor clamp bulkhead to the motor well bulkhead. The resulting box is very strong and stiff. Instead of using a flat panel, though, I used a separate panel for each side, so the slop well could drain to a single center point, emptying into the motor well through a hole in the motor board. This requires more nailer strips, but first we have to make the lines.

First we find the lowest point of the slop well. This will be on the centerline below the motor. It needs to be low enough to stay out of the way of the motor’s steering cables, if applicable. For me that was about 4.75” below the top of the motor board, 4” below the top of the bulkhead.

I also assumed motor steering for the outboard sides, in case I ever wanted it. Knowing the position of the motor sheaves, I can determine where the springs and sheaves for the cable will anchor. The vertical frames I added provide a spring point for anchoring steering hardware, and we know from OMC’s literature that the anchor points should be vertically within 1.5” of the motor’s sheaves. Closer is better, but I marked the maximum.

These points allow me to determine the upper surface of the aft edge of the slop well deck, so it won’t interfere with the cables. Don’t forget this line is the top surface. You need to make another line below this line by the thickness of the plywood. I was going to use ¼”, but I decided 3/8” would be prudent. This is the kind of place where a swimmer climbing back into the boat can trip and put a foot through it. 3/8” is plenty strong enough and doesn’t weigh much more for such a small deck.

In this photo I enhanced the slop well lines. The small Xs on the vertical 2x2 frame are where the motor cable sheave and spring get anchored.

Now we need to decide on the fore-and-aft slope of the slop well. I decided that 5 degrees was enough, but that it had to be 5 degrees when the trailer was parked. Probably more like 7-8 degrees when the boat is level. I used my clinometer to measure this angle, though a level and protractor would also work. Note how I held a straight scrap of wood against the clinometer to transfer the line to the opposite bulkhead.

Be sure you transfer these points with the clinometer lined up parallel to the centerline. Otherwise you might end up trying to twist plywood. It doesn’t like that.

With points transferred at each side and amidships, then can be connected to form the lines for the forward edge of the slop well decks. I transferred the line for the nailers instead, skipping the upper line entirely. Then it’s a simple matter of connecting the lines all the way around. Here’s the enhanced photo again.

Now we need the correct bevels so we can rip nailer strips. This seems like a real brain bender, but really it’s not. I found a piece of scrap wood, broke it to length and wedged it between the fore and aft bulkheads so it’s upper surface lined up with the nailer lines. Then I could measure the bevel from the aft bulkhead and side.

To get the bevel correct, the leg of the bevel gauge that is on the bulkhead must be perpendicular to the nailer line. It’s easier if use a square (or any handy rectangular box) to draw such a line. You won’t have enough hands to hold yet another tool. Be sure to record and label bevels immediately. On the deck is easiest if you’ll be painting it anyway.

Only two bevels? Not quite. Those two take care of the sides, front and back. You get the rear bevel by subtracting the 15 degree tilt of the motor clamp bulkhead from the front bevel. But we still need a nailer to serve as a “spine” where the panels join in the middle. If I had a tablesaw at home, I might have cut a concave double bevel to do this. But with only a circular saw I thought it better to cut two separate strips and fasten them together. This bevel can be measured directly off the motor bulkhead – between the vertical centerline and the nailer line.

Fastening the nailers is nothing complicated. But pre-drill or these little sticks will split. This is just as well, since we should really dry fit any assembly with so many bevels. It’s a lot of opportunity for error, so I’d like to know it all fits before getting out the glue.

This is also a good time to dry fit the hatch frames for the access between the aft cockpit and the newly created storage under the slop well. These frames should be on the forward side of the motor well bulkhead. That way you have a place to install screweyes for the shock cord that retains the hatch cover. I think it is easiest to draw the hatch opening on the aft side, cut it, then frame it.

The decks are easiest to make by spiling, just like we did for the bulkheads. (They are already white because I was using scrap that was already painted.)

Good, it all fits. (Except that bit under the wide decks where you really have to piece it together later.) But before we glue it into place, we should fit the scupper that will drain this slop well into the main motor well. I used a scrap of 1” copper plumbing pipe I had laying around. I’m sure ¾” would be fine. I cut the hole so it would be a little below the level of the slop well decks. This is why we install this part before the decks. We don’t want any water pooling there, right on a glue joint. I bored a pilot hole, then finished with a spade bit. After shining up the metal with sandpaper, I glued it in with PL400. I would have preferred epoxy putty, but epoxying temperatures were still months away.

Here you can save some effort if it’s warm out. Glue in the nailer strips and hatch frames. When these cure, trace the hatch openings onto the hatch cover stock while you can still get to both sides. Then prime and paint all this new construction, including the underside of the decks. This means much less mess trying to paint all surfaces of the inside of a closed compartment. Unfortunately, like I said, it was too cold to paint. So I had to deal with a well-painted arm in the spring.

Drain holes

It may seem strange to bore drain holes in an open motor well. But the water tends to collect just forward of the slot when the boat is on the trailer. These holes allow it to drain. Be sure the end grain is thoroughly sealed with epoxy. Better yet, epoxy in a piece of 1/4” copper tubing like I did. It’s hard to see in the crud that collects in the corner, but it’s there.

These holes are small enough that they don’t let in much water underway, but they are plenty to drain the motor well at rest. This is much better than having to reach around a greasy motor to sponge up a couple ounces of water every time I trailer the boat or it rains. And obviously it’s much better than letting water collect there.

Draining the Corners

Since we added the full-height motor bulkhead frames, there is a little pocket behind each where water will tend to collect. This is bad. One way to drain it would be to cut a limber hole through the frame itself. This works, of course, but it’s a real pain to paint the inside, and you have to remember to cut such a hole before installing the frame. I wasn’t 100% confident of where it would need to be, so I went the other way.

By elevating the deck in that pocket, water is forced to drain. I did this with some small triangles of scrap plywood. I used one screw and “gooped” them into the corners with PL400 and a single deck screw.

They look better once they’re painted. Still not beautiful, but functional and unobtrusive under the side decks.

Aft Hatches

Now we have two unventilated spaces to the sides of the motor well. This is bad in a wooden boat because it encourages rot. We need to add new hatches to replace the ones we removed. This time I did it the smart way and set up the motor and steering and everything and went boating with it. Then I could draw on the decks where I wanted to put gas tank chocks and hatch openings. I think it’s important to do it this way, because your first idea might not allow for the movement of the motor or steering cables.

Normally I’ve been pretty satisfied with the Michalak-style plywood hatches, but this situation is a good case for using a ¼-turn access plate. I don’t need to really store stuff inside these air boxes now that I have the much more convenient hatches under the slop well. More importantly, I probably shouldn’t store stuff there, since the motor and fuel provides plenty of weight there already. I’ll want that air to support the machinery high and dry if I ever capsize. But I still need an access plate so trapped moisture doesn’t rot the hull.

On top of that it is pretty easy with such a motor well to wind up in a situation where the hatch has to be under a fuel tank. I’d avoid this because it is an extra step when trailering, but a flush hatch might be handy if you ever make a long trip under power and need to carry extra fuel.

Finally, a flush hatch is good here because this is where swimmers climb back aboard and there’s already too much junk back there with the machinery. It is one less thing to trip over in an area where you really don’t want to trip.

And as it turns out, Duckworks has some decent access plates that are cheap enough for even someone like me to consider them. (I nearly fell out of my chair when I checked the prices of comparable products through one of the major marine suppliers.)

They are easy to install too. Trace the hatch and cut a hole that fits it but doesn’t pinch it. Screw it in lightly with some silicone RTV sealant. After the silicone cures, tighten the screws a little to put the “gasket” under tension. (Thanks for David “Shorty” Routh of for this technique.) I put them right next to the motor because the fuel tanks can’t go there or they would interfere with the motor’s steering.

Again, be sure that the hatches drop into the hole without forcing them. If you have to force it into place, the hatch will deform and it will be difficult or impossible to attach the cover. Speaking of the covers…

On the product page, Duckworks points out that these access plates can be difficult to open when you can’t get your wrist at just the right angle. To remedy this problem, Chuck screwed on scraps of wood to provide a better handle. I wanted to keep them relatively flush, so I did it the other way around. I made a “key” from scrap plywood to increase leverage. The keying is repeated on the other side, but rotated 90 degrees, so I can always find a workable angle.

Of course flush hatches have their downside as well. When the boat is parked and they are open, rainwater is more likely to get in the compartments if it blows under the tarp. In practice it’s been less than a spongeful, so far.

Fuel Tank Chocks

Here’s the final touch. The fuel tanks are held down by three eyebolts and shock cord. The cord belays to the two on one side, both parts run through the tank’s handle, and an S-hook attaches the cord to the eye on the other side. If the eyes are close enough to the tank, they also serve as chocks to keep it from sliding around. Note, however, that these are 2.5-gallon tanks. You might need more than shock cord for the heavier standard 6-gallon variety.

Placing these tanks was trickier than it looks. It looks like there are many options for locating the tanks, but you can’t use most of them if you ever want to steer with the motor. I found that steering with the rudder was almost always just as good, but I still wanted the motor steering as a backup. So where you see them is really the only place they fit! I think this reinforces the idea that outboard motors are much better hung on the transom.

In any case this is an improvement over the earlier motor well. The motor can tilt up all the way and be steered with cables (maybe not so useful after all), all the “slop” drains freely from the boat both in the water and at rest, we gain back lost freeboard astern, and the hatches are actually useful.

On the design

In spite of my complaining, one shouldn’t imagine that I fault Bolger for the original design “flaws”. This is just one of the things that can happen when one tries to adapt a racing design for knockabout sailing, auxiliary, and power launch use. Had I fully thought out the different application I might have made these changes before actually building. Or I would have skipped the inboard motor well entirely.

Bolger remarks in Boats With an Open Mind that he doesn’t like inboard motor wells and only designs them when his arm is twisted. I think he’s probably right. Think twice before you decide that one of these monsters is a good idea. And if you find yourself twisting a designer’s arm, listen to him instead!

Rob Rohde-Szudy
Madison, Wisconsin, USA

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