Shoal keels

[MoodySabre]

A mate is looking for a bigger boat but can’t find a new or newish Dehler 36 which he fancies. He has seen a Dufor 36 which has a shoal keel. He knows nothing about that type of keel and how it compares to a fin keel.
Do they point as well? Any upsides or downsides.

 

[johnalison]

It varies a lot according to class. Some shoal keel boats have very shallow fins and the performance you would expect. My HR has nominally 1.5m cf the usual 1.8. I have sailed with and against sister ships with the deep keel and for the most part there seemed little difference. In lighter airs we seemed to do better, probably from a lower wetted surface. I’ve not done a thrash to windward in company but we seemed to point as well, though I suppose there may be a small difference in leeway. The only significant difference I have noted is a lessened resistance to rolling on some occasions when I have been able to compare with my sister-ships. The only occasion this was significant was when sailing through the Alderney Race with a free wind, when we tended to have the wind thrown out of our sails and the other boat was faster. In other ways, such as being able to carry sail, our shallow fin seems much the same.

 

[Martin_J]

I totally agree with all that Johnalison has said above.

I have the shoal keel Moody S38 (1.5m draft instead of the 1.8m draft).

I would say that generally when cruising, or even sailing round the world, you tend to not plan to set a long leg to windward if you can avoid it.. so in that respect the shoal keel may even be better for the majority of planned sails.

Notwithstanding the fact we did two Fastnet races, both of which were predominantly against the wind and were quite happy with performance both times. Crew on board would never have guessed.

The other advantages to a shoal keel are more options for anchoring in places like Newtown creek, getting over a cill on a rising tide sooner and being able to antifoul up to the waterline whilst ashore without having to reach too high.

Oh, and a small work platform you'll be able to polish the topsides whilst ashore, which isn't so easy with a deeper keel.

 

[Martin_J]

I also have a friend who asked the same question to me when they were looking at a modern Beneteau Oceanis 40.1 (that was the shoal draft 1.7m version instead of the usual 2.2m).

They went for it in the end and after a year with it, they are more than happy with the shoal draft..

 

[vyv_cox]

Me too. I have the shallow fin Sadler 34, 1.4 metres. It is very rare for us to be outpointed by anything, although we do have very good sails. A friend has another Sadler 34 with a deep fin but old sails. We outpoint him by 10 degrees.

 

[johnalison]

Me too. I have the shallow fin Sadler 34, 1.4 metres. It is very rare for us to be outpointed by anything, although we do have very good sails. A friend has another Sadler 34 with a deep fin but old sails. We outpoint him by 10 degrees.

That wouldn’t have applied to the Sadler 32. I have friends who had the fin and the lifting keel versions, but the shallow fin and bilge keel versions were distinctly poorer performers, which is why I said it depends a lot on the class. The downside to shore maintenance is that you have to stoop more with a shallow keel to deal with the a/f, though topsides are easier. I think it depends on where you sail. Channel sailors may value the slight advantage of deep fins, while I was grateful for my lower draft in many places. There are some designs with very shallow fins that just look wrong and it should be possibly to judge from looks without actually sailing a boat.

 

[Tranona]

Much depends on the design of the keel. Most tend to have more ballast than the "standard" keel with the extra weight at the bottom in a bulb. From what I can see the Dehler is not very shallow with 1,65, compared wth 1.85 of the standard. Doubt you would notice any difference in normal cruising mode. Sails and a folding prop have more impact on passage times than draft, but ultimate pointing ability given the same sails might be less.

I have had 2 shoal draft Bavarias. The first a 2001 37 was very shoal 1.4m rather than 1.9m chosen so that I could transit the French canals. In normal use it was fine, but did suffer in heavier weather, not helped by knackered sails and a lot of windage from bimini. The second was a 2015 33 1,5m rather than 1.95m was a much better performer under sail, but was a different design that was altogether better.

If the rest of the boat is OK the keel type would not be a deal breaker for me.

 

[Graham376]

We have a scheel keel (1.4m) Moody 376 and on one Biscay crossing in company with a deeper keel version, noted no difference in performance.

 

[Dockhead]

Keel depth -- and aspect ratio -- are crucially important for upwind sailing. The keel is a wing just like the sails are. The lift from the keel is just as important as the lift from the sails -- going upwind.

Downwind it's not important. So if you use the motor upwind, a shoal keel is fine.

 

[Laminar Flow]

According to the Delft keel study, done on a considerable variety of different keels, the time difference between the best performing deep keel and a much shallower, longish keel conducted in winds of 15kn and 25kn over an Olympic course (2/3 to windward), was 4% and 5% respectively.

It could very easily be argued that for a cruising boat that difference is immaterial, that it could also easily be the margin between a more competent helmsman and one of less experience and that the benefits of shallow draft, while cruising, easily outweigh the (slight) difference.

While edge of your seat, upwind performance might be crucial for racing, for cruising it is not. Being able to make that tidal window into a marginal port, finding a better anchorage closer in, visiting that special place others may not be able to go to is, at least to us.

 

[johnalison]

According to the Delft keel study, done on a considerable variety of different keels, the time difference between the best performing deep keel and a much shallower, longish keel conducted in winds of 15kn and 25kn over an Olympic course (2/3 to windward), was 4% and 5% respectively.

It could very easily be argued that for a cruising boat that difference is immaterial, that it could also easily be the margin between a more competent helmsman and one of less experience and that the benefits of shallow draft, while cruising, easily outweigh the (slight) difference.

While edge of your seat, upwind performance might be crucial for racing, for cruising it is not. Being able to make that tidal window into a marginal port, finding a better anchorage closer in, visiting that special place others may not be able to go to is, at least to us.

That may be true, but I think that many of us want to feel when sailing that we are not missing out on something that might help us pass that other boat. As I said, my boat compares well with its deeper sisters in speed, sail-carrying and pointing, and although there must be a difference, it has been something I could live with, especially as I had ordered the boat with this option, albeit at an additional cost of about £2,500. I guess that modern designers have learned from the mistakes of the past and are less prone to design the pigs of a few years ago.

 

[Tranona]

According to the Delft keel study, done on a considerable variety of different keels, the time difference between the best performing deep keel and a much shallower, longish keel conducted in winds of 15kn and 25kn over an Olympic course (2/3 to windward), was 4% and 5% respectively.

It could very easily be argued that for a cruising boat that difference is immaterial, that it could also easily be the margin between a more competent helmsman and one of less experience and that the benefits of shallow draft, while cruising, easily outweigh the (slight) difference.

While edge of your seat, upwind performance might be crucial for racing, for cruising it is not. Being able to make that tidal window into a marginal port, finding a better anchorage closer in, visiting that special place others may not be able to go to is, at least to us.

Totally agree. That kind of difference can be eliminated with a folding or feathering propeller. There is a difference between "round the marks" sailing and cruising passage making. With otherwise identical models of boat the difference over, say a 60 mile cross channel passage would be small. From my experience the losses from a shoal keel version are in ultimate pointing ability and leeway plus in heavier weather to wind, Neither circumstances form a large part of cruising life.

 

[Laminar Flow]

This is precisely why it is important to quantify the difference from one model to the other and why such research as done by the Delft institute is critical.
It is equally important that we compare apples with apples. The Delft study was done for 7 different keel types on the same hull. This did not include twin keel versions. The difference over a 4 hour time span and over the same course was a mere 10 minutes from best to worst.