Cutting into the side of the boat/deck for a door. Structural ?

[waynes world]

Hi all, i need advice here as this is not to be done on my boat but a chap that could do with a door in the side of the boat fpr easy access for his to get on board the rear deck. who is struggling a little.

I said i cold possibly help out with it and he has now sent me pics of what he wants doing.

It is single skin GRP on a classic Viking boat.

I can work out how to go about it but the main concern is if it will affect the structure of the boat.

A few pics of where the door wants to be put. The bottom edge can be just above the strake if need be, but i see it if it is there or below the strake it will make no difference really to the structural integrity of the boat..

No worry on the cables as they can be moved out the way.

thanks all

 

[neil_s]

Is this a canal boat? If so, then I doubt that hull strength is a major concern. I would resist cutting into the rubbing strake, though and also consider fitting an in-wale to retain rigidity in the hull where you cut away the topsides.

 

[waynes world]

Is this a canal boat? If so, then I doubt that hull strength is a major concern. I would resist cutting into the rubbing strake, though and also consider fitting an in-wale to retain rigidity in the hull where you cut away the topsides.

Yes it is a canal boat so no large forces on the transom/hull.

It would be fully braced, what do you mean by an in-wale ?

 

[William_H]

The whole strength of the hull is predicated on the gunwhale being intact right around the hull. I would suggest that to maintain hull stiffness You would need to surround the whole area of remaining skin with more GRP or even better carbon fibre to make effectively a U shaped support to the opening. This should be attached or in fact laminated on with epoxy.
Now just how much extra strength you need is a question. I am not sure that it is safe to say "not needed as it is only a can al boat." It is possible that turbulance in a lock, being stranded on a sand bar or even lifting from the water could demand that stiffness in fore and aft direction. In worse case you could break it's back without the integrity of the gunwhale and top sides. Boats are seldom designed to be stronger than necessary. I would be thinking in terms of 6mm extra GRP thickness for a distance of 15cms around the hole.
I would suggest this is a major mod and should not be undertaken lightly. Should it be done, would depend on the imperative of making the boat more accessible. Plus how long it is going to be needed. Cos I reckon the value of the boat will be diminished by the cutting. olewill

 

[Neeves]

The whole strength of the hull is predicated on the gunwhale being intact right around the hull. I would suggest that to maintain hull stiffness You would need to surround the whole area of remaining skin with more GRP or even better carbon fibre to make effectively a U shaped support to the opening. This should be attached or in fact laminated on with epoxy.
Now just how much extra strength you need is a question. I am not sure that it is safe to say "not needed as it is only a can al boat." It is possible that turbulance in a lock, being stranded on a sand bar or even lifting from the water could demand that stiffness in fore and aft direction. In worse case you could break it's back without the integrity of the gunwhale and top sides. Boats are seldom designed to be stronger than necessary. I would be thinking in terms of 6mm extra GRP thickness for a distance of 15cms around the hole.
I would suggest this is a major mod and should not be undertaken lightly. Should it be done, would depend on the imperative of making the boat more accessible. Plus how long it is going to be needed. Cos I reckon the value of the boat will be diminished by the cutting. olewill

+1

I'd buy a set, or two sets, of steps, with hand rail - interior and exterior - or have them made. It will be cheaper (value of vessel) and safer (in terms of the integrity of the hull).

I would not buy a vessel that had one of the major structural components compromised - by a couple of (with no disrespect) amateurs (underlined as you have come here for advice). I imagine canal boats are not in short supply on the market and I think your modifications might make the vessel unsaleable.

But I am sure others will disagree.

Jonathan

 

[alexrunic]

I personally don't think this is a good idea. It might be strong enough for canal use, but what if you need to crane out? The compressive forces when craning out can be quite large especially if the yard doesn't have a proper boat hoist or they don't use a spreader beam. I also agree with the point about making the boat un sell-able.

If you would like some professional advice I would speak with a surveyor I'm sure this idea will make there toes curl

 

[bedouin]

I tend to subscribe to the "don't do it" school. All those angles in the fibreglass you would be cutting away add a lot of rigidity to the structure. If you do you would need to add additional stiffening to replace that you lose - maybe a plank of ply across most of the transom (with it's own cut out).

Seems to me it would be pretty simple to make better steps

 

[Simonpk]

The profile of where you have marked is step like, without having to cut out a hole in the side of the boat, how about some sort of hinge just above the rubbing strake, make a step that follows the contours of the coaming & side deck (where you've marked out), that folds out & rests on the pontoon. Folds back into where you have marked.

I don't know if I've explained it as I see it though.

 

[fisherman]

I suspect that even if you had a long gangplank the step down inside would still be an issue. I would (almost) happily cut down as far as the rubbing strake, but then would fix a horizontal stiffener inside the hull top, fore and aft as far as possible, and at least as wide as the whole gunnel section including the top. Then vertical formers from this inside the box gunnel either side of the gate. This would replace all the horizontal stiffening removed and form the top step.

 

[neilf39]

Apart from the structural integrity aren't you going to remove the ability to lower the cockpit canopy by cutting short the track runner? I would have thought a removable short passarelle hinged via slots on the outer deck would be the best bet. That would give a relatively shallow ramp up. It could be used on either side or even the stern if deck fittings were put at each location. On the inside fit a step half way up to allow a step down in. That could even be made to hinge up so out of the way when not needed.

 

[GrahamM376]

I seem to remember many years ago someone had done something similar for disabled access - maybe a Colvic hull? If the boat builder is still in business, they would be my first contact for advice. I'm sure it can be done but must be able to withstand impact and lifting. to the same extent as original build.

 

[oldharry]

I would go with the rest. You will be cutting through a main structural component of the boat. Canal boats do have to be able to withstand heavy internmittent loads - two boats swirling about in a lock can put a fair bit of pressure on the gunwhales for example. Its a different set of stresses to a seagoing boat, but none the less important to be taken into account. 10 tons of steel Narrow boat coming alongside perhaps a little less gently than intended, can apply several tons pressure! A lifting sling will compress the hull. The shape of the gunwhale which you are proposing to cut away has been engineered to withstand these pressures safely. Structural changes like this need to be thought through very carefully by someone able to calculate the resulting weakness. Also the end result would devalue the boat very substantially: who would buy a boat that has been chopped about like that! You might also have difficulty getting insurance on such a badly mutilated hull, which is of course mandatory on the canals.

A step up and over, or some sort of passerelle arrangement would be far safer.

 

[Lon nan Gruagach]

What I see of the existing structure is a box section (mebby 3" by 8"), the hood tracks are screwed into this.
As such a simple beef up the surround isnt going to cut the mustard.
So, what to do? (I hate it when answers are "you didn wanna do that")
Cut the hole as required.
Cut the box section at 45 degrees so a new box section forming 2 inverted Ts with a single top(bottom) bar (around the new hole) can be added. The new box should be deep enough to sit on the hull and have gusset plates where the stems meet the top(bottom) bar and where the stems meet the original box.

 

[Caer Urfa]

You will 100% reduce the structural integrity of the boat and other than an idiot no one would not buy her in the future, seams drastic but I would change the boat 'IF'

this is absolutely required to something more suitable, plus IF you did one good wave would flood the engine bay and don't say it will never happen

leave well alone as for sure someones going to say 'who the hell did that'

 

[Quandary]

Surely this is not a job for an amateur, either to carry out or advise on. If the boat is sold on at some stage without survey heaven knows where it might finish up.
Though I am all for DIY and I am not a fan of surveyors who have to be ultra conservative to protect their PI premiums, it at the very least needs to be carried out by a competent boat builder who fully understands structures and the stresses that the boat might be subjected to. Proceeding on the basis of comments from strangers who have viewed a couple of photos for 2 minutes is foolhardy.

 

[Uricanejack]

Is it impossible? probably not. Is it a good idea? probably not.
You will be seriously affecting the longitudinal strength of the boat. Could this strength be replaced by other means? probably.

It looks like the goal is to achieve restricted mobility access. If I was going to try and do this I would consider modifying the transom rather than the side of the boat. Why. The transverse strength lost by cut out can probably be replaced much more easily.
Stainless checker plate?
It will work when stern to. Not so easy when alongside. An extended rear swim grid may help.

 

[fisherman]

A 'swim platform' (though not many want to swim in a canal) could have a simple gangway clipped on either side. Is the transom accessible from inside?

 

[jwilson]

Hi all, i need advice here as this is not to be done on my boat but a chap that could do with a door in the side of the boat fpr easy access for his to get on board the rear deck. who is struggling a little.

I said i cold possibly help out with it and he has now sent me pics of what he wants doing.

It is single skin GRP on a classic Viking boat.

I can work out how to go about it but the main concern is if it will affect the structure of the boat.

A few pics of where the door wants to be put. The bottom edge can be just above the strake if need be, but i see it if it is there or below the strake it will make no difference really to the structural integrity of the boat..

No worry on the cables as they can be moved out the way.

thanks all

Certainly COULD be done, but to be safe would need a LOT of stiffening. The gunwhale and cockpit coaming are very significant parts of the overall rigidity of the hull. Even if done well the boat will be effectively more or less unsaleable afterwards.

 

[neil_s]

An in-wale is a gunwale, but inside the boat. If you kept the outside rubbing strake intact and reinforced the hull inside to compensate for the lack of bracing due to the cockpit moulding, I think it would be OK. A big modification to a boat will reduce it's re-sale value as others say, but I think we are talking of an old boat, no longer of great monetary value, here. We are also talking about making it possible for somebody who is a bit creaky to continue enjoying the boat. Would it be possible to make the cut out piece of cockpit moulding fold inwards on hinges and become a step down? I guess if you kept it, it could be glassed back in when easy access was no longer necessary!

 

[Plum]

I would echo what a few others have said. Cut a door in the transom and fit a full width swim platform at pontoon hight. Transom doors are fairly common on motorboats, just look around any coastal marina for ideas. This arrangement will also enable access from either side of the boat. The swim platform could have a guard/hand rail along its aft edge. If its all done well I don't think it will devalue the boat at all.

Www.solocoastalsailing.co.uk