Fixed keel in the place of a swing keel

[sporades]

Considering buying a Manta 19 sailboat (an old boat from the Schochl boatyard, a Miglitsch design) which had a swing keel that the owner replaced with a fixed keel supposedly to make the boat more seaworthy, with the fixed keel being considerably heavier and deeper than the swing keel. The original draft of 91cm is now a draft of 1.35m. The keel is iron with a lead bulb at the bottom.

He sailed it along the Croatian coast to Montenegro and says it works well, but looking at how it moves the centre of resistance (?) forward so much I wonder how this has affected the way the boat behaves. I will attach a photo showing the original keel design and the replacement. Does it look suspect? Does anyone have experience of similar keel replacements?

 

[dunedin]

Not sure who your insurers are likely to be in that location ….. but I suspect in the UK it may be extremely difficult to get anything other than third party insurance for a major amateur modification like that.
Unless the previous owner was a structural engineer the huge extra leverage of the new keel could cause issues with the attachment area and hull structure.
In spite of forum doom-makers, very few keels have fallen off un-modified cruising yachts, BUT a very significant proportion of keel losses have been after modifications have been made to the original design.

 

[oldbloke]

Free advice is worth what you pay for it, so here goes.
The CLR on the original boat looks a long way back, the current keel potion looks more normal. Anyway, easily shown on test sail.
Re structure, a small keelboat like that will hardly be pushing the limits of materials science. If the keel box to hull join isn't showing signs of strain now, it probably won't. The keel box was probably engineered to be weight bearing originally.
Dunedin is probably right about insurance, however as I hope you're not considering more than a thousand or so (mostly for the trailer) then 3rd party is all you want

 

[sporades]

My mind hadn't got to the possibility of losing the keel. Too preoccupied with things like the boat feeling all out if balance and too much weather helm because the new keel is further forward than the original.

 

[KevinV]

The drawing doesn't have the swing keel all the way down. The fixed keel looks in the right place, faired in and with a bulb attached. As for the soundness of it I can't possibly judge, nor the effect of stiffening the boat beyond what the rig and it's hull attachments was designed to take.

I'd be suspicious about why someone would be selling it so shortly after having done so much work to it - I wouldn't touch it.

 

[LittleSister]

I have always thought the Manta 19 was an attractive and nicely thought out boat, and it was on my list of 'would like to have' boats some years ago. (I have some brief 'review' comments on the design from PBO or some other magazine somewhere. I can't lay my hands on them right now, but will post here if I find them soon.)

The following website (see link below) about Manta 19s has a picture of a larger boat, the Sunbeam S22 ,from the same Schochi boatyard (but a Van de Stadt design?) which is said to be similar to the Manta, at least in appearance and lines , and the fin keel on that is swept backwards and presumably has the lateral resistance further aft than the amateur modification you are looking at for the Manta 19, even though the drop-keel version of the Sunbeam S22 has its keel further forward than the Manta.
Manta History | The Manta 19 Trailer Sailer

Personally I'd be very wary about the particular Manta you are considering, concerned about structural integrity, insurability and that it would be harder to eventually sell on again, as well as how balanced the rig/hull/revised keel is.

The drawing doesn't have the swing keel all the way down.

I believe it does, actually. Somewhere I have details, but if I remember correctly from all those years ago, the drop-keel arrangement is all under the hull, as it were, and doesn't have the typical box intruding into the cabin for such keel, so it's quite shoal draft.

Re structure, a small keelboat like that will hardly be pushing the limits of materials science. If the keel box to hull join isn't showing signs of strain now, it probably won't. The keel box was probably engineered to be weight bearing originally.

As per my comment above, i don't think it has an internal keel box as such. It's not just a matter of (downward) weight, but also of the lateral forces, which would be significantly increased, I think.

 

[KevinV]

I believe it does, actually. Somewhere I have details, but if I remember correctly from all those years ago, the drop-keel arrangement is all under the hull, as it were, and doesn't have the typical box intruding into the cabin for such keel, so it's quite shoal draft.

You are quite right - just a 450mm difference between raised and lowered - page 4 of the assembly instructions, here:

Assembly Guide | The Manta 19 Trailer Sailer

I was thinking it was more like a Tartan 36, which I have experience of

 

[justanothersailboat]

I can imagine two situations where someone might make a major keel modification.

Either they know enough to know they know they've done it right...

...or they don't know enough to know to worry about whether they've done it right.

I know one or two people I would happily buy a modified keel from, a few more I would run away if they even mentioned they were modifying their own keel, and many who know enough to know they shouldn't start.

But with the low cost of old 19 to 22 footers there's got to be a decent chance of finding one with a keel originally made to your liking, surely?

 

[chriscallender]

Considering buying a Manta 19 sailboat (an old boat from the Schochl boatyard, a Miglitsch design) which had a swing keel that the owner replaced with a fixed keel supposedly to make the boat more seaworthy, with the fixed keel being considerably heavier and deeper than the swing keel. The original draft of 91cm is now a draft of 1.35m. The keel is iron with a lead bulb at the bottom.

He sailed it along the Croatian coast to Montenegro and says it works well, but looking at how it moves the centre of resistance (?) forward so much I wonder how this has affected the way the boat behaves. I will attach a photo showing the original keel design and the replacement. Does it look suspect? Does anyone have experience of similar keel replacements?

What is it like inside the cabin ? Having owned 3 lifting keel boats, and one fixed I'd say the downsides of lifting keels are
1) The keel box takes up a lot of cabin space and makes it harder to move from one side of the cabin to the other
2) There's a massive hole in the bottom of the boat where the keel lifts, which opens into the cabin above the water line. Knock downs in a lifting keel boat are likely to be pretty nasty meaning I wouldn't want to go offshore in one.

Actually I reckon there's a pretty high likelhood with a lot of designs that if you inverted a lifting (not swing) keel boat that the keel would drop right out its slot and potentially go straight through the cabin roof. Maybe that's just my paranoia but I wouldn't risk being out in heavy weather in one, and its what I always thought about. Also, little nuisance things like I used to occasionally get a crab come intio the boat via the keel box.

Where I'm coming to with this is that if the modification completely removed the keel box inside the boat (and had been correctly designed/implemented to a high standard - which I can't judge) I can see that it is an improvement in some ways, but if it is just that a fixed keel has been wangled inside the lifting keel box and somehow locked down you'd just be getting the worst of both worlds. No ability to reduce your draft and still an annoying/dangerous/nuisance keel box inside the cabin.

Another question on my mind would be whether the boat is safely able to dry out on that keel (looks ok in the photo on the trailer though - it doesn't look like too much weight is sitting on the pads).

Chris

 

[scozzy]

Walk away, surely spoilt for choice in the sub 20ft market with plenty of boats keenly priced that may be tired,might need rigging upgrades or other fairly straightforward fixes but the big stuff like... the keel! Is intact and does what it should when it should, I doubt I could cast off without worrying about that particular modification!

 

[William_H]

I would say that the movement of centre of lateral resistance will not make a lot of difference to sailing performance. The aft slope of the keel is to move the keel under the centre of gravity for when on hard.
The stub keel being still fitted will not be an efficient keel shape fro going to wind ward. The ideal being a keel to hull shape like a dinghy with centre board. Still probably ok in practice.
Re comments by Chriscallender regarding vertical drop keels. My 21 fter which I have sailed for 45 years has ballasted vertical drop keel. I keep a bolt through the aft to of keel box which is to stop any chance of keel dropping to ceiling in an inversion. But in practice it is primarily there to take the load when I run aground stopping the keel kicking back and up damaging the trailing edge. The 5/16 inch bolt does get bent absorbing some of the energy in stopping the boat.
I have done pull down test on the boat and at 90 degrees ie mast horizontal the boat floats high such that windows barely wet. (no crew) Certainly no chance of water getting in to cabin via the open top of the CB case. ole'will