How will this boat behave in a seaway?

Hello everybody,

I am new to the forum, this is my first post. I have about 25 years of sailing experience on different boats, but none in boat design. I read a couple of introductory books, and I can tell the difference between a bluewater cruiser and a club racer, but that's it.

I have recently purchased a 1975 custom IOR 3/4 Tonner sailboat, "Rapid Transit". The boat was designed by Ben Lexcen (aka Bob Miller) and built by Custom Yacth Services, Australia using c-flex and vinylester. LOA:34.3, BMAX:10.6, BWL: 8.9, Draft: 6.0, Displ:12600

Anybody has information on the history of this boat? There isn't much info about Ben Lexcen's designs other than the famous wing keel of Australia II.

I am very curious about how this boat will behave in a seaway. So far, I only had a chance to sail her in very light winds (Bf2) which did not reveal much except that she seems to be quite tender. She is currently on the hard and I am fitting her out for offshore cruising.
My previous boats had long keels (Folksong 25, Marieholm 32, Golden Hind 31). All of these boats tacked well, had a confortable motion, never pounded upwind, but they were quite slow and had limited maneuverability (especially the Golden Hind which needs a soccer field to turn around). Now, I am wondering how my new boat will behave compare the old ones.

When looking at hull shape of "Rapid Transit" (I attached several pictures from different angles) this is what I see (correct me if I am wrong):
- Compared to more modern designs (racer/cruisers) a big portion of the hull is underwater, and the ratio of the hull and the fin keel is very high (almost 50:50).
- Unlike a canoe shaped hull, she has relatively deep sections. Deep V forvard, rounded but still fairly deep amidship, and flattish aft
- Pretty narrow at the waterline
- The bow line from amidship to the bow iscurving up nicely
- The rudder is small
Considering these features I think (and hope) that the boat will have a good turn of speed, especially upwind. She will have a relatively confortable motion. It will (hopefully!!!) not pound upwind. It is quite tender. As it is usual for these earlz IOR boats, she will have a tendency to round up and broach downwind.

I would appreciate any input from the expert boat designers of the forum.
Thanks in advance.

Best regards,
Den

 

she's a pretty classic early to mid 70s IOR hull. which means upwind she's a rocket ship though tender and heeled 15-25 degrees
downwind she's a broach coach.
on reaches she'll corkscrew through the toughest wine bottle.

 

I agree. That is typical of the era. Those designs with pinched ends and slack bilges were made to beat a formula and not for real speed or seakeeping.

 

This one isn't as pinched as some:


But then again the joke about SJ24s is that they go downhill just as fast on their sides as right side up.

I remember doing a windy race in Long Island Sound back in 1980 on a custom 30' IOR machine the year after the Tartan 10's came out. We were flying a blooper for stability and the T10s who started ahead of us were going downwind:

Wobble stb
Wobble port
Wobble Stb
Wobble port
BROACH...
come back up
Wobble Stb
Wobble port
Wobble Stb
Wobble port
BROACH

Seriously something like 5 broaches by one of them on the downwind leg.

 

Agree with the others about the tendency to broach of IOR boats of the period. Don't know anything about this particular one. On a spinnaker reach the IOR boats were a real hand full and if you survived a hard reach without at least one broach you were lucky.

 

I am no expert on hull design, my expertise is engineering, but I have seen the IOR boats in action when I crewed for others during local club racing.

They actually perform pretty well in all conditions except for the aforementioned tendency to broach. If you are not in a race you can avoid this I suspect by never running straight down wind but rather always sail as some angle to the wind, jibing as necessary, and do not drive it too hard with a spinnaker (it tends to bury the bow, and lifts the rudder out of the water, particularly when heeled, which causes the broach). This particular one appears like it would want to heel over easy, though that actually might have a less tendency to broach perhaps since it will not lift the rudder out of the water as much when heeled as compared to the more beamy IOR hull designs. You might also reduce the risk of the broach by putting a deeper and larger rudder on it, this will also help the steering response as well.

I suspect it would actually handle heavy chop well, that sharp bow will not want to pound as much as your typical full bow common on pure cruiser hulls.

common recommendations for a deep water cruiser is not to use a spade rudder like you have, there is a high risk of strike damage when in the shallows and it could pick up sea weed when under way. you can perhaps strengthen the rudder installation, and reduce it tendency to pick up weeds, by placing a well reinforced fin or skag in front of the rudder to protect it from a strike. Though that is a major operation, but I might consider it if i was doing other changes or heavy maintenance or repairs to the hull. For nominal conditions that keel and rudder configuration should be fairly responsive and efficient, putting a larger rudder would improve low speed steerage as well as reduce the tendency to broach.

 

Thank you for taking the time to reply my question.

I know that the stock answer to the performance of an IOR boat is that it goes like a rocket upwind and she's a broack coach downwind. But this is certainly a generalization. When I compare my boat to other IOR 3/4 Tonners ot the same era (Morgan 33T, C&C 3/4T, Finngulf 34, Carter 3/4T, UFO 34 etc) I can see some similarities, but at least as many differences. Not to mention that some of the IOR boats have very good reputation. One example is the UFO 34. yachtnet.co.uk writes this about the UFO 34:
"Whilst many IOR yachts of the period had a reputation for poor handling, the UFO34 was both fast and virtually vice-free, and the class became successful both as racers and as fast cruisers, many boats being used exclusively as cruising yachts."

The two most striking differences between my boat, "Rapid Transit" and other IOR 3/4 Tonners is the much deeper hull of Rapid Transit. Forward she has deep V sections with a nicely curving profile between the keel and bow in contrast to other boats which usually have flattish sections and profile forward. I hope that this will make the boat relatively comfortable going upwind winthour pounding. The lack of pounding upwind is a very important feature for me. I sailed on my friend's Jeanneau Sun Magic 44 on the Med and that boat pounds badly. She pounds even downwind, which makes sleeping in the aft cabins impossible. Same is for another friend's brand new Van de Stadt Forna 37.That boat tries to shake your teeth out.
What makes a boat pound sailing upwind? How can I say by looking ata design whether it pounds or not?

The other feature of Rapid Transit that is different from other IOR boats is that a big portion of the hull is underwater. This, I guess is the result of the narrower, deeper sections. What is the effect of this? Will this make the boat slower? Perhaps roll less? Or makes her more confortable in a seaway? etc.

I don't plan to make major modifications (like adding a skeg) to the hull at this point, although the unsupported rudder worries me a bit. It however seems very strongly built. The rudder shaft is 1 3/4 inches solid SS and it is supported by a substantial bulkhead all the way from the hull to the deck. Of course most damage takes place where the shaft enters the hull...

 

A combination of two things make a boat pound: when the periodicity of her transitioning through the waves is shorter than her natural harmonic pitch oscillation , combined with a hull shape that has a rapid increase in buoyancy.

Essentially you fall off the wave or slam into the wave (because you are out of phase with it) and the relatively flat or rounded bottom of the boat hits the water and immediately (relatively so) stops. This was never a behavior of IOR boats because they all tended to have fairly fine ends. What they would do instead is pitch a lot.

this tends to be slow off the wind, which is why that hull shape was abandoned when the rules stopped encouraging it. Now whether you can sleep in the fwd cabin during this is a different matter since the result is that the bow is moving up and down in very large arcs.

Narrower and deeper sections are part of what make the boat more tender, and they are also part of what make for a broach coach. Essentially what happens is that the boat has to get immersed quite deeply before full buoyancy/RM kicks in. And usually that means the other end of the boat (the stern) is lifting well out of the water just as the maximum rotational force is generated by the immersed (bow) section

Or alternatively because of the fine stern, the bulk of the quartering sea is already under the boat when finally the stern starts to lift. So you have a bit of a "submerged cork' effect on the stern and midships which spins the boat to weather. Either way you have a heavy corkscrew motion going.

So I suspect you won't see her pound much, but I think she's going to be a handful off the wind in anything over 15kn of breeze.

 

I find that short handing these IOR boats tends to produce a two speed boat. On or Off. My Catalina 38 will either go 7.5 knots to windward in 25 knots, or 2.5 knots. And nowhere in between. IOR boats are jib sensitive as a general rule, and cruising them does not relieve you of the need to carry a bunch of jibs - which you will change often. The corkscrewing is manageable with reasonable powering. Yours doesn't have the big hips of some later boats. If the only loose headsail you have is a drifter for light air, she should be a blast off wind compared to regular cruisers. The main thing you will miss is the rail meat. These boats were designed for rail meat. If you plan on multiday reaches, invest in a jug farm so you can shift your ballast accordingly.

 

Hi Don, I can tell you A LOT about Rapid Transit. I owned her for 10 years, selling her in ~2007. When last I heard she was in Florida. Please contact me via the forums email facility.Dave.

 

There you go Don... perfect... he can tell you all you need to know about her handling in a seaway!