The Internal Outboard Engine and The Engine Box

 Outboard motors offer the advantages of compactness and portability with concomitant ease of removal for  servicing and repair over an inboard counterpart. No portals need to be made in hull for water ingress and egress, or exhaust fumes. In the case of sailing craft retraction of the propeller is a nice feature.
 However major disadvantages are how they affect the attitude of the craft, vulnerability to being swamped, difficulty to service or repair on the craft, theft and vandalism, that until the event of the four stroke version, noisy and smell and reliability were significant factors.
Of course there was the inboard / outboard which was initiated by Volvo and then by the major outboard manufactures. Their point was that the engine could be put anywhere along the lubber line and so related the
engines weight to the craft's attitude. Ease of fitting and the fact that the propeller's position close to and below the gear box negated the need for space and long shafts were other advantages.

It was these issues that coursed my mind in developing the engine box. Although I haven't researched it  I can't imagine for a moment that its particularly new. I have been on and seen small sailing craft where an outboard has been on pinioned lift on the transom where it could be lowered and raised as needed and also
where portal in the counter has been made to drop and accommodate an outboard. In both however exposu re to green water, general slop and driving rain made them vulnerable.
I suppose it would be germain to define 'an engine box' at least in the terms that relate to my boat.
An engine box is a delineated confine for an outboard to enable its easy movement in and out of the water below the craft and facilitate and ideal retracted position which will maintain a low centre of gravity, be able to be stabilised, and provide good exposure for fresh water flushing ( a good discipline ), maintenance and repair. Inevitably the outboard should be one whence that exhausts through the propeller but 'bleeds' on some engines will mean a diversionary pipe to take the exhaust to the bottom of the well. Similarly, the egress of water from the engine needs to be diverted somewhat from the spout that throws the water laterally from under the engine cowling. Of course this is really a directional issue  as long as this is down into the well and, importantly, vitally in fact, can be seen.

Arrow 1. indicates the usual exit for engine water. Here, in a functioning position, water would be filling the boat over the top of the engine box but has been rerouted in the cowling to arrow 2. where it will be well down in the engine well but above the cut-off seal and therefore easy to view at any time.
An exhaust bleed at arrow 3. would exit fumes into the boat, normally these would be going aft in the wake of a boat, and have been rerouted to exit at arrow 4., where an aluminium spigot accommodates the yellow re-routing tube seen in the picture below. At this level it is below the cut-off seal.

I chose a long shaft outboard to give me the broadest scope for manoeuvring the parameters for designing
the engine box and fit it into the boat.
At the outset it was one of my hopes, allowing that the boat goes through the water well, power on - power off, that it should go well under sail. Therefore a low centre of gravity for the retracted engine was quite high on my priorities as well as bringing its ballasting component forward where the bulk of the buoyancy in my boat's design lay.

In the absence of CAD I made full size mock up of the engine profile in thin ply and using this with thin battens worked out a the profile that would allow vertical lift of the propeller and subsequent forward incline of the engine.


The profile of the engine in the retracted position. The fine clearance of the propeller at the left margin (representing the aft limit of the engine box) shows easily.

The  profile being rotated down shows the flanges on the front of the shaft casing touching (bearing on) the
slippery dip profile of the box. The rectangular section, centre right , the would be transom in a normally situated outboard, has now moved up and backward.

The engine has now entered the water with its cavitation plate a couple of centimetres below the bottom of the boat represented by the bottom margin of the background sheet.

Boarding Ladders

This boat seems to offer lots of challenges and  none quiet so awkward as that of getting into and out of it.
Its displacement is as yet uncertain and so therefore is the free-board.
I estimate all up but crew free the weight will be 1100 kilos which, as the water mass it will displace, means 1.1 cubic metres. This approximates to the volume of the boat beneath the floor board runners and is a foot above the keelson.
Thus the free board will be some 4 ft at the stern, 3 amidships and rising to 4 again forward and except at  the stern the hull, being sans bilge, cuts in deeply and offers no vertical purchase to board. Also the decking slants up towards the lubber line. The combined result means a difficult boarding from a dinghy along side or from a pontoon. From the briny itself it would be near impossible.
So for safety and convenience I have solved this by providing a permanent ladder on each side, just rear of midships, which is hinged so that it can folds into and under the deck when not in use.
Below is a general view of the ladder between the forward shelf and rearward seating flat against the hull and
out of the way.

This shows some detail of the hinged wing supports similarly laying flat against the hull and the bottom section of the ladder is seen folded in and under its upper part.

Here is seen a retrieval lanyard and bash plate where the ladder will come to rest and below shows how hauling it from outside the boat causes the ladder to swing up, out and over the deck.


The ladder can now be seen unfolding completely. The hinged wing supports are swung so as to engage the hull where they keep the ladder 'vertical'  prevent it from swinging under the hull.

Some detail of the ladder across the deck and engaging the bash plate. The yellow cordage seen in these pictures is shock cord and the way it is strung causes a 'click fully open' effect on the bottom rung but a closing effect when folding is started.

The white line that shows along the hull will be where the boot top will be. The bottom of the ladder comes close to this and hopefully will allow someone in the water a chance to get on board.

Problems using Sikaflex

As best I can determine the Sikaflex 291 i  represents the pinacle of marine sealants but certain drawbacks exist over silicones, not the least being that it goes off quite quickly ( 30 - 40 mins at 15degrees - my estimate ) This is not bothersome for small jobs but when many tens of fastenings - screw, washer, washer, spring washer, nut and Nylock nut combinations have to be brought home then this becomes an issue.

The housing as shown needed to be fixed but allowing for some flexing of the hull and indeed Sikaflex seemed ideal. Where my helper friend and me founded was not looking up existing data on the handling of this sealant. Clean 'offable' before setting, at an exponential with time, but once set it become a extreme hindrance. The obvious use of gloves became out of the question for in the handling of the fastenings the glove material pulled itself off the fingers and onto the components so it became bare fingered.
Available data suggested that it could only be removed from the hands, once set,  using a razor blade, not exactly what the doctor ordered.

 The above shows the 'sandwich' that was to constitute the seal. The boat hull, to be the meat between the 'bread', so to speak, is missing here but shown below.

The above shows how the sealant was laid to encapsulate each hole through which there would be a  fastening.

   
After tightening up the job was horrendously messy and like our hands below it  took hours and great patience to remove. The cured sealant, by now cured,  needed four days before all traces left our hands despite washing, scrubbing and the use of all reasonable solvents and abrasive creams. I think this is the time that it takes for the skin of the hand ex-foliate the dead surface epithelium.

 This view underneath the boat shows pretty much the same picture.

I haven't solved the problem I've shown and it looms again in the business of sealing the engine box against the hull in much the same way. However the use of a gasket, especially a compressible one, such that could be made from Neoprene Foam, rides high on the list. This compresses by one third and is available as sheeting in a range of thicknesses up to 6mm from Ram Gaskets. I have asked for samples and this company is sending me some.