Personally, I'd say it all comes down to what you want to do with the boat.
I'm not sure anyone can argue against the superior hydrodynamics of rudders that emerge from the hull bottom, either on a fixed stock or as retractable rudders in drums. You can also get away with less strength in the stock/blade this way.
One thing that would worry me would be the drum bearings. They're do-able, but there's less expertise, and fewer manufacturers in this area, when compared to a rudder stock. And these rudders will be enduring more sailing forces than a normal monohull or multihull drum rudder.
But that's a minor point. Half of these boats qualifies as experimental as each person makes changes to the design. To worry that something hasn't be done before is to eliminate the Harryproa.
The collision issue would be the major one for me. Let's say you hit a
whale, submerged shipping container or log, or uncharted sandbar, while doing ten+ knots.
a) With the external rudders, the mechanism will break away. The best case is that you simply re-attach the rudder with a new "fuse", and then go on sailing. The worst case is that you can't use the rudder, and will instead have to steer with a backup mechanism. Neither case involves structural damage, a weakening of the boat, or a hole in the hull.
b) With internal rudders, the following might happen:
- The rudder mechanism breaks the hull, water enters, and the boat no longer works.
- The crash box functions, so there's no sinking, but there's still some structural damage, and there's still water in part of the hull.
- The breakaway rudder fails properly, but now can no longer be raised or lowered due to its post-crash
shape, and there's still a likelihood of damage to the bearings.
In all these cases, there's a good chance of structural damage, water in the hull, damage to the bearings, and an inability to repair the damage while at sea and return to sailing normally.
---
I grounded out two years ago and ruined my daggerboard supports when I let someone else helm for an hour. While I was able to get them repaired, but the truth is that I was lucky. And had we been doing ten knots, my deck would have buckled under the stress. That would have been a very unfortunate day on the water that could have involved injury and great expense.
So the idea of having every foil below the waterline kick up is more important to me than ever. That means either a Harryproa, a Dragonfly tri, or a Seacart tri (I think Seacarts can do this, but I'm not sure). Given the huge difference in price between
the three, the Harry is the easy winner.
This is not an argument to use external rudders. I'd like to see people develop the drum rudders because they fascinate me, and also because I'd consider drum rudders myself (albeit with the drum mounted on a pivot that can allow the entire mechanism to kick up).
And if you want to go fast, avoid steering balance issues, have an easy up/down system, and stay away from experimental designs, the drum is a good choice. Especially if you're not going to make an ocean passage.
But I'm a fan of being comfortable with the worst-case scenario. It might not be likely, but it does happen. I'll personally go with an external option.
- Mike
On 6/13/2010 7:43 PM, Gardner wrote:
Hi,
I am curious about your objections to drum rudders. The seem to be a proven technology, since they are in so many production boats (Hunter, Menges, Gunboat, maybe?).
I understand the point about collisions, and it also seems like there might be an issue with getting enough chord on the rudder, but those are the only drawbacks that come to mind. What am I overlooking?
- Gardner
Sent from my iPad
G'day,
I don't think much of in hull rudders, and even less of drum rudders, but they are not too difficult to make from composites and acetal ball bearings from McMaster Carr. You will need some turned alloy or steel (better) rings to use as moulds. Let me know the width of the hull and I will do some drawings.
rob
On Mon, Jun 14, 2010 at 5:17 AM, Gardner Pomper
<gardner@networknow. org> wrote:
Ok, that is at least 10 times the price I am willing to pay. Anyone have any ideas on what it would take to make one (well, two, actually <grin>)? I would like to think that there would be an easy way to just build some extra rudders if you do hit something and pull out the old one (or push it down through) and replace it with a new one and (maybe) repair the old one at your leisure.
Is this the system that Rapscallion was going to use? I remember his having in-hull retractable rudders, but I don't remember a mention of a drum, so it did not seem that they could steer while retracted, which turned me off.
- Gardner
2010/6/13 Helmut Müller
<hmueller@otenet. gr>
I got an answer in 2008 from Paul Amon for the inboard rudder:
Each unit as installed on a Melges 32 would be around 6900usd with hard anodized bearing, rudder, tiller, housing.
Quite expensive, no solution for us.
Cheerio