aussie mast rake specs

Several weeks ago one of our forum members mentioned that the aussies are using much more mast rake on their H18s and that it improves performance somewhat. I am familiar with mast rake measures from mast to tang (max 107") suggested in the hobie 18 performance manual(Berman) but, have any of you come upon specific measurements used by the aussies? Wishing to experiment>>>>Deejay Thanks

Do you have low profile main blocks? If not, you probably won’t be able to rake back that far.

sm

Hi guys. I am the Aussie with the mast rake. You do not need low profile blocks. In fact I have a strop on my mainsheet system.

The way we measure the mast rake is with using the trapeze wire extended forward to the bridle tang and aft along the gunwale.

I have posted numerous photos on my boats Facebook page of how to measure this and where my mast rake measurement is. It has a dedicated photo album on my boats Facebook page. Remember to “See All” so you can see the various photo albums. See link in my footer below. I’m willing to share everything so let me know if you need any more information after you have viewed the photos (or if you don’t have Facebook. My page is public).

Please see Facebook photos before reading on.

- rig tension on
- mast rotation to be fore-aft
- no sails hoisted
- Boat on flat level ground
- add 1’ length of rope to trapeze ring dogbone
- measure and mark the length where the rope extension touches the bridle clevis pin
- walk the trap wire aft along the boat until it touches the gunwale. It will generally touch the gunwale around the rear beam area. In strong wind it will generally touch the gunwale aft of the rear beam.
- however, with my boat, I have it raked so far aft that it reaches aft of the rear end of the gunwale and we then measure it touching about 1-2” down the transom.
- to achieve this you will need a longer forestay. The convenient way to add length is to simply make a longer top forestay from the hound shackle to the swivel fitting.
- the more you rake the mast back, the more you must slide forward the jib cleat cars in the track.
- be mindful that with maximum rake you may also need a new jib spreader patch higher up to protect the jib.
- the more you rake the mast back, the more you need to tuck your rudders under to balance the helm.

Enjoy.

_________________
John Forbes
Hobie 18 Reimagined
Sail # 490
Boat name: 18@heart
http://www.hobie18.fun
https://www.facebook.com/Hobie18catamaran/

An H18 already has too much weather helm when sheeted hard and raking the rudders doesn't change the drag from the excessive angle of attack needed to keep the boat on target. It just makes it easier on your arm by moving more of the rudder surface in front of the axle line where the water flow eases the force needed to hold the rudders off center.

I always run my rake as far forward as possible until probably 15+ knots when the bows digging at full speed downwind becomes an issue and then I take it the mast back a few holes on the plate.

Maybe if these old mainsails didnt stretch so much it would be possible to effectively flatten them and move the sail balance forward more to kill the helm. The ability to change the sail shape is pretty limited. On shore yea I can do some stuff but once there is pressure in the sail it's back to having too much camber.

I think having a reef point might be good in moving the sail balance where I'd want it in heavier air.

I'd have to see some very controlled experiments to believe that heavy rake makes an overall improvement in all conditions. It wouldn't on my boat and how I sail. Differences in helm style and consistency, weight balance, sail age, sheeting tension, etc could make enough of a difference to create a false result here.

John Forbes and TAMUmpower Thanks for both your replys, very interesting thoughts on mast rake......DJ

Hi TAMUpower. I'm at the extreme back with mast rake in all conditions (0 knots to 25 knots) Never change it. Raked the rudders under until the helm is neutral (I like very slight weather helm) and our boat is a rocket ship. We applied the same logic on our Tornado and this translated directly through to the H18 - if you don't know the results let me know coz they are pretty self explanatory. I have many, many photos in albums on my boats own Facebook page showing how much mast rake we have and how we measure it - plus loads more photos of info. I appreciate everyone may not agree with it, but for us, it certainly is untouchable against every Aussie H18.

_________________
John Forbes
Hobie 18 Reimagined
Sail # 490
Boat name: 18@heart
http://www.hobie18.fun
https://www.facebook.com/Hobie18catamaran/

Around here the boat setup would make little difference in the ability to be "untouchable". H18 is much more of a seat of the pants boat. And I'm pretty sure someone that usually wins could easily run full forward or rear rake and still be at the front. Why not switch your rake and see if you are suddenly last?

Around here the boat setup would make little difference in the ability to be "untouchable". H18 is much more of a seat of the pants boat. And I'm pretty sure someone that usually wins could easily run full forward or rear rake and still be at the front. Why not switch your rake and see if you are suddenly last?[/quote]

Hi Tamu: I like your style. I wish your logic was recognised by others in the Australian fleet. Apparently some think we are untouchable because we use a non genuine trampoline and my jib blocks are located 4” different to everyone else’s. But that a different topic.

Hi All: the sail shape can be altered greatly by shaping the battens. We have posted recently on the Hobie 18 Scene Facebook group how we shape our battens and what compression weights we recommend.

Mast rake alone does not solve the problem. It is the combined effort of mast rake, rudder rake, ruder style jib sheeting angle, batten shape, spreader rake (aft hole), diamond tension and mainsail Cunningham tension that all contribute to the end package. Plus new sails greatly help. Hobie 18 jibs become much fuller in shape with age and that is not fast. The mainsails loose their leech tension with age and that restricts good height upwind. Overall acceleration is limited with aged sails (more than 3 years old).

EPO3 rudders make a huge improvement to the helm. After we changed rudders and got the balance correct, we now don’t need to kick the windward rudder up ever. The helm is completely balanced and the boat therefore has no ‘drag’ from the steering. It took a while to get the rudder set up correct but once you find the sweet spots the boat becomes a dream to steer.

The Hobie class rules do allow sails to be re-cut if you wish to invest in trying to get some life out of your sails. I’ve never done it to a Hobie sail but I’ve done it to many Tornado cross cut sails over the years. You would need to re-set the bolt rope and luff tape and also get “take-ups” done on the leech at most batten pockets and that would give some extended performance.

Larger, additional corner patches will also assist in the safety of the sail by helping it not fail at the clew and/or the 9th batten pocket. We have seen one or two mainsails fail across the second bottom and third bottom batten pocket with age and a reinforced clew area can prevent that from happening.

Enjoy.

_________________
John Forbes
Hobie 18 Reimagined
Sail # 490
Boat name: 18@heart
http://www.hobie18.fun
https://www.facebook.com/Hobie18catamaran/