Mills IRC 39
2006 December 6
December 2006
This 39-footer was designed to fit a specific rating gap for local racing and the designer chose to put the boat at the top of the class in terms of potential boat speed. If any given class has a rating spread there is always an advantage to being at the top of the spread. The bigger, i.e. faster rated, boat should have a slight boat speed advantage that will allow it to clear its air quicker at the start and have more tactical options on reaching legs. The small boat in the class will often find itself sailing in the bad air of the bigger, faster boats to the degree that its rating advantage cannot make up the difference.
The IRC is kind to draft and stability. This IRC design has just over 8 feet of draft and a huge, long bulb. There is no bow overhang but there is quite a bit of overhang aft where it can do some good as the boat heels. Remember, you have to immerse volume if your overhang is going to do any "work" to increase sailing length. The freeboard is really high on this design. I suspect the IRC is also kind to freeboard. I can't say with that freeboard that this is a pretty boat but in a workmanlike way it is handsome to my eye and has a muscular, capable look to it. There is about 2.83 inches of spring to the sheer. The entry is very fine and the stern is reasonably beamy but not exaggerated. The D/L is 179.66 and the L/B is 3.34. The relatively high D/L will make for a fast and stiff boat upwind in a breeze.
This deck plan shows a long cockpit with an open transom. Crew weights have been kept well forward. It's slow to have crewmembers camped in the stern of the boat. The helmsman sits well forward and there are twin wheels. With twin wheels you can move from the companionway hatch to the transom without climbing onto the side decks. There is a life raft well in the forward end of the cockpit sole. There are cockpit seats and low seatbacks. The primaries are forward, notched into the low coaming. The jib sheets at an 11-degree angle and the chainplates are outboard at the deck edge.
The interior layout is Basic Layout A: V-berths forward, head adjacent to hanging lockers, settee berths, galley to port, nav station to starboard and port and starboard quarterberths. The settee seatbacks hinge up to form upper berths. It doesn't get much more straightforward than that. And the secret is, it works. The engine, a 28-horsepower Yanmar, is located directly below the companionway. You could cruise this boat very comfortably and quickly.
The rig looks huge. I is 51 feet and P is 51.5 feet, giving an SA/D of 24.26. Mainsail roach is modest by today's standards as the IRC does not like roach. It also does not like running backstays so these spreaders are swept 20 degrees and curved. I'm not sure what curving the spreaders does except that it might allow the shrouds to move aft while providing more athwartships support for the mast. The sailplan shows a jib with about 100 percent LP.
Designing racing boats to a handicap rule is not only about designing the fastest boat. It's about designing a boat that is faster than the rule thinks it is. Successful design in this area requires careful analysis of where the boat will be raced and the prevailing conditions and courses. Mark Mills tested more than 30 hulls on his computer before arriving at this design to see which rule-friendly design components produced the fastest boat for a given rating. Mark has been right a lot lately.
IRC racerr
This 39-footer was designed to fit a specific rating gap for local racing and the designer chose to put the boat at the top of the class in terms of potential boat speed. If any given class has a rating spread there is always an advantage to being at the top of the spread. The bigger, i.e. faster rated, boat should have a slight boat speed advantage that will allow it to clear its air quicker at the start and have more tactical options on reaching legs. The small boat in the class will often find itself sailing in the bad air of the bigger, faster boats to the degree that its rating advantage cannot make up the difference.
The IRC is kind to draft and stability. This IRC design has just over 8 feet of draft and a huge, long bulb. There is no bow overhang but there is quite a bit of overhang aft where it can do some good as the boat heels. Remember, you have to immerse volume if your overhang is going to do any "work" to increase sailing length. The freeboard is really high on this design. I suspect the IRC is also kind to freeboard. I can't say with that freeboard that this is a pretty boat but in a workmanlike way it is handsome to my eye and has a muscular, capable look to it. There is about 2.83 inches of spring to the sheer. The entry is very fine and the stern is reasonably beamy but not exaggerated. The D/L is 179.66 and the L/B is 3.34. The relatively high D/L will make for a fast and stiff boat upwind in a breeze.
This deck plan shows a long cockpit with an open transom. Crew weights have been kept well forward. It's slow to have crewmembers camped in the stern of the boat. The helmsman sits well forward and there are twin wheels. With twin wheels you can move from the companionway hatch to the transom without climbing onto the side decks. There is a life raft well in the forward end of the cockpit sole. There are cockpit seats and low seatbacks. The primaries are forward, notched into the low coaming. The jib sheets at an 11-degree angle and the chainplates are outboard at the deck edge.
The interior layout is Basic Layout A: V-berths forward, head adjacent to hanging lockers, settee berths, galley to port, nav station to starboard and port and starboard quarterberths. The settee seatbacks hinge up to form upper berths. It doesn't get much more straightforward than that. And the secret is, it works. The engine, a 28-horsepower Yanmar, is located directly below the companionway. You could cruise this boat very comfortably and quickly.
The rig looks huge. I is 51 feet and P is 51.5 feet, giving an SA/D of 24.26. Mainsail roach is modest by today's standards as the IRC does not like roach. It also does not like running backstays so these spreaders are swept 20 degrees and curved. I'm not sure what curving the spreaders does except that it might allow the shrouds to move aft while providing more athwartships support for the mast. The sailplan shows a jib with about 100 percent LP.
Designing racing boats to a handicap rule is not only about designing the fastest boat. It's about designing a boat that is faster than the rule thinks it is. Successful design in this area requires careful analysis of where the boat will be raced and the prevailing conditions and courses. Mark Mills tested more than 30 hulls on his computer before arriving at this design to see which rule-friendly design components produced the fastest boat for a given rating. Mark has been right a lot lately.
|
|
Comments