Deck Step Rig Tension leaking hatch

[Darrel_Walters]

Hi
Looking for a little guidance

This winter, I had all new rigging for my 38foot 10 year old boat.

over the last couple of months I have noticed that my Lewmar hatch, 14 inches aft of the mast had started to leak, as the hatch and the others were crazed I decided to purchase all new one and go about the task of changing them.

The stern one is fine then I took the amidships one out to find that the deck had convexed across the hatches leading edge to the mast, The thickness of the GRP in this area is approx 8 mm but you can visually see support in the GRP for the mast etc under the head lining. it then thins down to where the hatch is.

I contacted the sail company who rigged the boat for me and they had advised that they had tensioned the mast to between 12 and 14% of the breaking strain, I had mentioned to them that the deck had bowed as mentioned above, but was unable to suggest if this would be deemed OK or if there is failure of something.

I have now fitted the new hatch which in this case now uses 5 and 6mm bolts instead of screws, this has reduced the bowing to approx 4mm over its 500 mm width. You can noticeably see a slight bow in the hinge side but the hatch seems to be working fine and sealing OK.

I know you have to be careful with deck stepped masts and I know you should not over tension the rigging.

Is what I have noticed normal or does anyone have some sound advice to belay my concerns

Many Thanks

 

[webcraft]

Hi
Looking for a little guidance

This winter, I had all new rigging for my 38foot 10 year old boat.

over the last couple of months I have noticed that my Lewmar hatch, 14 inches aft of the mast had started to leak, as the hatch and the others were crazed I decided to purchase all new one and go about the task of changing them.

The stern one is fine then I took the amidships one out to find that the deck had convexed across the hatches leading edge to the mast, The thickness of the GRP in this area is approx 8 mm but you can visually see support in the GRP for the mast etc under the head lining. it then thins down to where the hatch is.

I contacted the sail company who rigged the boat for me and they had advised that they had tensioned the mast to between 12 and 14% of the breaking strain, I had mentioned to them that the deck had bowed as mentioned above, but was unable to suggest if this would be deemed OK or if there is failure of something.

I have now fitted the new hatch which in this case now uses 5 and 6mm bolts instead of screws, this has reduced the bowing to approx 4mm over its 500 mm width. You can noticeably see a slight bow in the hinge side but the hatch seems to be working fine and sealing OK.

I know you have to be careful with deck stepped masts and I know you should not over tension the rigging.

Is what I have noticed normal or does anyone have some sound advice to belay my concerns

Many Thanks

If the hatch structure is taking some of the bow out of the deck as your post suggests then it will be under enormous strain - not what it is designed for at all.

I think it is quite obvious that your rigging is tighter than it was before and probably too tight. Borrow a tension gauge and check the tension - most sources say the tension on the lowers should be about half that on the cap shrouds.

If the relationship between caps and lowers is OK then just unwind a few turns all round until the hatch stops deforming and see how she sails. If you can't tell the difference and the leeward cap shroud is not visibly sagging when you are hard on the wind in a good breeze then that should be fine.

- W

 

[Salty John]

The rig tension is about right at 12% -14% of the breaking strain of the wire (actually on the low side), but only if you have the design wire sizes. If the boat has been fitted with bigger wire diameters than the designer contemplated then you'll have too much load on the mast. This doesn't seem likely but could possibly be the case.
Often there is a mast partner below the mast to transfer the load to the keel; or there is a ring beam arrangement to transfer the load to the hull.
It's not unusual for boats to distort when the rig is tightened, you hear stories of cabin doors jamming when the tension is increased, for instance. The problem is to how much distortion is allowable in the design.
You need to slack off your shrouds a few turns and see if distortion reduces. I'm inclined to think that if you loosen up enough to remove all distortion your rig will be too loose, which brings its own problems. Think more about strengthening the deck than sailing with a loose rig.

 

[Bosun Higgs]

Deck stepped mast is a bit of a misnomer since your boat is designed so that all the loads in the mast are transferred via the mast support pole inside the boat down to the hull where they "meet up" so to speak with the loads of the rigging transferred down through the hull. The deck should not be under any real load instead just being squashed a bit in a sandwich.

If the riggers have gone at it like idiots, they could have caused this distortion by bending the whole boat but this is unlikely - after all, whatever static load they put on the boat it has to be able to stand a fair bit more as the rig comes under under sail.

So the first place to look is at the mast support pole and step inside the boat. Has something given way there? Has the support in the deck sandwich between mast and support pole given way? In my view its likely a structural issue not a rigging one

What sort of boat is it?

P.S. Whilst you will get some hull distortion under rig loads ( the famous toilet door syndrome) this is worse the further you get away from the mast because the movement is bigger. And we would be talking a mm or so, not 4 or 5mm

 

[William_H]

Mast support structure

As said you need to loosen the rigging and examine the mast support post or bulkhead for condition especially at the bottom and top. If it seems Ok then you need to force some packing ie 6mm thick between the top of the mast support and the under side of the cabin roof. (or between the post and the keel) This will then take the downward compression without forcing the cabin roof down hence the cabin roof should remain the same shape and hatch remain undistorted. good luck olewill

 

[Darrel_Walters]

To all thanks for the update

Can I suggest a bit more detail
The boat is Maxi 38 with in mast furling, with swepe back spreaders 7/8

My thought has been, that if the forstay when it was re rigged was slightly to long, then by tensioning the shrouds you would increase the tension on the forstay, in doing so you would then increase rack, and change the angle of incidence to the keel support back and therefore, increase pressure of center to the rear of the mast support.

The Chain plates are exactly in line with the start of the hatch.

As the boat is not really a racing boat but a fast cruiser, does the above seem plausible. also It has been hard to flatten out the sail to reduce leach flutter, and the kicker is on as hard as it can be.

does the above seem logical

Many Thanks
Darrel

 

[ianat182]

Your forestay tension and mast rake is done via the backstay, if fitted, also you are putting a lot of load along the boom with the kicker on hard and thus causing increased compression via the mast.
Do you mean that you have adjusted the original setup by the rigger to increase the tension of the shrouds, if so, then there is your problem I guess.

ianat182

 

[garvellachs]

Maxi 38

There's a maxi owners site to ask if others have had the problem. And I would contact Maxi/Nimbus too to ask their advice.

Is the hatch leading edge bowed downwards towards the keel in the middle or upwards (you mention "convexed" - sounds like upwards).

Forestay length affects rake very noticeably - compare photos from last season and this. We installed a new forestay this year and the rake looked wrong at first until we got it the right length again (I asked Van de Stadt for an original design drawing to get it right - they were brilliant).

 

[Darrel_Walters]

A noted on the convex of course in hindsight it should be concave bowed inwards (depressed)

I have since spoke to SD marine, who at first suggested to look for any signs of compression which I have already done and no signs are visible.

Needless to say this has only happened since the new rigging has been fitted, which ment that the mast came down to re rig and then put back up again, something may have moved and to be honest if it weas not for the changing of the hatch, quite possible I would not have noticed.

There can only be two reasons for this
A the rigging is not correct or
B Failure in the support for the mast

As the mast is the only thing that has been touch logic seems to lend itself to the rigging as opposed to the boat.

Would help if anyone would concur that my thoughts may be correct.

Regards
Darrel

 

[Bosun Higgs]

Needless to say this has only happened since the new rigging has been fitted, which ment that the mast came down to re rig and then put back up again, something may have moved and to be honest if it weas not for the changing of the hatch, quite possible I would not have noticed.

There can only be two reasons for this
A the rigging is not correct or
B Failure in the support for the mast

As the mast is the only thing that has been touch logic seems to lend itself to the rigging as opposed to the boat.

Would help if anyone would concur that my thoughts may be correct.

Regards
Darrel

I cant see any way in which the rigging lengths could be wrong and cause this problem. Nor can I see how any reasonable level of rig tension could cause it. At 5mm or so, its simply too big.

The centre of the deck is designed not to come under compression from the rigging and mast except for a bit of squashing between the heel of the mast and the top of the compression post.

I can understand your view that it must be something to do with the re-rigging but the only thing I can suggest is to loosen off the rig a bit and see if it makes a difference.

Difficult to make any other suggestion without seeing the boat. If your background isnt something like engineering then it may pay you to have a word with a friendly qualified surveyor.

 

[pvb]

Doesn't sound like your rigging is over-tight, but it may well be tighter than it was before. Riggers often say that owners rarely tension rigging adequately. I'd caution against loosening the rigging - this can accelerate fatigue failure at terminals - and it's not the solution to your problem.

The structure of the boat should be sufficient to support the mast loads without deformation. It sounds as if the support structure inside the boat has degraded, and that having properly-tensioned rigging has revealed the defect.

I had new rigging earlier this year. Prior to that, the fibreglass under the mast step had deflected downwards. I had the yard cut out the fibreglass under the mast step to investigate. It was thought that some plywood packing had compressed. The plywood was removed and the hole filled with solid resin and re-gelcoated. With the new rigging fully tensioned, the area under the mast step still looks solid.

 

[Darrel_Walters]

Hi all
That were kind enough to make comment and others who may have read this thread, but indeed I did contact a surveyor to look at the boat. And to my surprise when he carried out a few simple measurements it was established that only the front half of the mast was supported from the post up from the keel. The back of the mast had no support. It was also established that apparently there was about 12 inches approximate of rake, therefore indicating the forestay was a bit to long and the rigger may have racked up the back stay tension increasing the rack to tighten up the forestay, therefore increasing the load on the back of the unsupported mast.

The rigger and the surveour has agreed to retune the rig, so the mast has maybe only two inches of rake and therefore applying more force to the center of the mast.

In regards to the mast support we can only imagine that if the mast was a standard hoist the sails jobby..... Then it's foot print would have been under the support more so, however, my mast in in mast furling and the foot print would be around ten to twelve inches.

One the rig is retuned we will re examine the support and if so engineer a new bracket for it.

What is surprising is again, if true, maxi the quality manufacture has made yet another design boo boo that is two on one boat that has cost it's owner more 1000.00 of pounds

So sad
Regards
Darrel