Videos of fitting a Bow Thruster on LM

[johnc]

The following link is to a series of videos relating to drilling large holes for a bow thruster on an LM. You have to log onto facebook to view the video which is on the Danish LM Website
www.facebook.com/groups/579994708771153/permalink/2657662051004398/

[johnc]

Hi Chris, the link I have posted is to the LM klubben.dk facebook page. I just tried it and it works ok however I am a member of the Danish Facebook group. As you would expect, almost all the posts are in Danish with a few exceptions. I use Google translate so that I can post in the group and they seem to understand my replies.
To be honest its a set of scarry videos as the guy is drilling a 150 to 200 mm hole in his boat but it is worthwile joining the group as there is quite a lot going on..

When you apply to join the group, it asks if you have an LM.
I think this is a link to the home page.
www.facebook.com/groups/579994708771153/?ref=share

I have also come across a Youtube video made by the same person which covers the operation of drilling out the hole.

m.youtube.com/watch?v=hYGrTOOmyH4

[chrismunson]

It worked! The issue was I tried it on an Android machine. I have a large collection of holes I have drilled in my boat, a couple are fiberglass, most are plywood from creating vent openings in the head door, battery compartment, and the 'box' that surrounds the refrigerator. Also installed small circular hatches in any sealed space, such as under the settees, for inspection and ventilation.

[Sula]

Eek!

My boat has gone in the shed today to have something like that done! 

The one in the vid looks too close to the lower edge of the hull for my taste and manufacturers' recommendations. I think they should have either canted the powerhead forward to enable the tunnel to be higher, or selected a smaller thruster.

[jandane]

Sula...Not a problem. On my 27`er it is almost the same. The tunnel is being plastered with fibreglass to inside and outside of the skip and in the end becomes a part of the structure

[oceandancer]

Hi All,
You may be interested to see the blanks cut from my boat to fit the bow thruster tunnel.
Interestingly the engineer seems to have cut a central hole and has used some form of electric saw to scroll outwards from the hole and around the edge rather than use a giant holesaw, as in the video.
He must have used a template as both pieces are so similar in size and shape.
I didn't see him do it as I was talking to another engineer at the stern about cabling. By the time I looked the tunnel was in and was being glassed up - no more than 20min from go!

You will note the thickness of the pieces - over 13mm! The layup is dense without any visible voids and the gelcoat seems to be about 1.5mm thick. I wonder how this compares with more modern construction.

Let us know how it all went Sula.

Regards

Mick

       

[Sula]

Mar 15, 2020 14:59:11 GMT oceandancer said:

He must have used a template as both pieces are so similar in size and shape.

Mick, thanks for the info and pics.

I very much doubt a template was used as the holes will be a different shape for every combination of boat and tunnel size and tunnel position.

The way I have seen it done (in pictures, but not in the flesh) is that small pilot holes are made, their position depending on how the particular thruster body fits inside the boat, and in light of the recommended clearance distances of the tunnel from both the waterline and the lower edge of the hull.  Once the pilot holes are made a 'final' check can be made both on those clearances and that the holes are truly horizontal.  (Any adjustment at this stage will require new pilot holes, but would not be disastrous.)

To mark the shape and size of the (non-circular!) holes to be cut for the (cylindrical) tunnel a gadget like a giant pair of compasses is used.  A long rod forms a 'central' leg which is passed from outside on one side of the boat through both guide holes, and the the other leg of the compasses holds a marker pen at the required tunnel diameter distance from the 'central' leg. As the 'compasses' are rotated the required elliptical-ish outline shape is marked on the outside of the hull. The process is then repeated for the other side of the hull.   

Once the required hole shape outlines are marked out, the hole is cut using an electric saw, starting out from the pilot hole (just to save drilling another), then following the marked shape outline.

p.s. Having gone to the bother of writing all that, I was Googling trying to find a picture of the 'pair of compasses' contraption I described, and came across this page which has not only a picture of the contraption, but pics and explanations of all other stages of the process, too! (And it's from the boatyard where mine is being done!)
southwoldboatyard.co.uk/2017/10/18/bow-thruster-nicholson-39/

 

[Sula]

And another way of doing it -