Mike and Rick: 

    Thanks for the responses.........  Performance is great, however my interest is in long term voyaging, not weekending and vacation trips from a shore base with an occasional longer crossing as seems to be more typical.   Payload matters, not because I need a lot of conveniences of home, but because supplies, spares, and tools add up far faster than most folks seem to realize, and I believe they fail to count many items.     Including just crew weight including clothing and shoes, bedding, and other personal items, dinghy, ground tackle, and many things one might consider part of the boat because they have been "permanently installed".    looking at one multihull designed for 4 people, the difference between design empty displacement and waterline displacement was only 1500 lbs.   With 4 crew members, and their personal items, 1200 lbs seems a safe bet.... bodies, clothing, foul weather gear, safety gear, etc.     That leaves 300 lbs for everything else, including food and water!    Many of the older factory builts simply do not have readily available published figures.  The result is that most multihulls are I suspect overloaded most of the time.    The larger "condocats" are so loaded up with convenience junk, that the payload for the size of the boat is pathetic. 

    My seeming obsession with payload is automatically translated by some folks into a desire to carry lots of conveniences, entertainment systems and junk.    The truth is actually the opposite, I am inclined toward the spartan.   What I DO care about is the ability to carry a reasonable complement of tools and spares to the extent that I can effect repairs and maintenance under most circumstances both at sea an in some remote ill equipped port.   When living aboard long term while voyaging,  safety, reliability, comfort, low upkeep, etc,  would seem to be more important that performance in most circumstances, the exceptions being dodging weather and major storms, and making coastal day hops that are right on the edge between being a day sail or and overnighter.   The latter is especially relevant when sailing solo in coastal traffic areas. 

    It seems that multihull designers either focus on performance, or on floating condos... the exception of course is Wharram designs that do not seem to excel at anything other than having lots of deck space.

                                                                                                                            H.W

On 8/13/19 8:23 AM, Mike Crawford mcrawf@nuomo.com [harryproa] wrote:

 

Owly,

  If you want maximum weight carrying capacity for a given length at low speeds, a catamaran is probably a better choice.  Partially because of whetted surface area, and partially because you can situate the boat weight, crew weight, and rig fore-aft to balance out the loads (at least in moderate seas).

  If you're looking to go closer to wind speed, or exceed it, and/or sail in bigger seas, then there are advantages to the asymmetric hulls -- basically everything Rick said.

  To recap, there are three primary advantages (at least to me):

    - At speed, the ww hull is largely unloaded, giving you the speed and sea-kindliness of the long lw hull.

    - The very slender wave-piercing lw hull ends allow the loaded hull to punch through seas instead of pounding up and down, while the semi-unloaded fatter ww hull is riding on top with less force on it.

    - When tacking either to windward or to leeward, the hulls will be interacting with seas more or less at the same time, so you'll pitch, but not corkscrew.

---

  It's not so much about top-end speed, though the HP design is impressive in that area, too.

  It's more about what effective speed you can maintain without getting beat up.  If you look up multihull reviews or stories with "corkscrew" and "hobby horse", you'll find a lot of info about how unpleasant it can be to sail a short-and-light multihull in bigger seas.

  The combination of the unstayed rig, which bends to dump power in gusts,and can go to neutral at any time, with the asymmetric hulls, allows for a higher average speed, with more safety, in more conditions, with less unpleasantness.

  You might be able to beat it with a purpose-built unidirectional multi and an experienced crew, but everyone would have to maintain peak alertness, and they'd still have to accept the punishing boat motion plus the increased risk of capsize or other failure.  There's not much you can do when a gust comes while your boom is pinned on the shrouds and the mast is painting circles in the sky.

        - Mike

Rick Willoughby rickwill@bigpond..net.au [harryproa] wrote on 8/13/2019 4:35 AM:

 

The HP is symmetrical to the lateral axis so your question needs some interpretation.  

The HP is a performance oriented displacement vessel.  As speed picks up, the ww hull unloads; the drive and drag align and the long slender, low buoyancy hull becomes very powerful with ability to drive through waves with minimal pitching.   The ww hull skips or bounces over the water acting as a counter balance to the sail heeling moment. Its effective displacement reduces as the speed increases simply because the need for righting moment increases with the speed increase.  

HPs have the advantage over a longitudinally symmetrical multi-hull in that the sail area presented to the wind reduces by virtue of the lw hull increasing draft with increasing wind load and boat heel.  The shorter ww hull certainly reduces the tendency to torque the entire boat when beating.  The lw bow can be well buried and beginning to lift about the time the higher volume ww hull hits the wave and begins to lift.  The lw hull buries in the back of the wave while the ww hull leaves the wave.  Going to weather there is little tendency to roll.  Similar condition when the HP is tacking downwind; with both hulls leaving the wave at the same time while the lw hull burying into the back of the wave and begins to rise at the same time the ww hull gets to the back of the wave.  It is possible to experience annoying roll on the 18m HP if running dead downwind.  The annoyance is due to the mast being loose in its deck bearing and it flogs if the boat rolls to the ww side and there is no lateral wind load on the rig.  It is much more pleasant reaching downwind and also slightly higher VMG if frequent shunts are not required.  

A shunt is a very easy task on a HP.  There is little flogging or snatching of sails in a normal shunt.   When tacking a longitudinally symmetrical boat, the sails inevitably flog going through the wind and many headsails are not self-tacking; in a gybe the mainsail inevitably snatches as the boom goes through the wind. 

Something that people familiar with sailing slow boats need time to appreciate is the significance of apparent wind.  Most HPs are capable of boatspeed exceeding windspeed, the upside of a long, low volume lw hull.  That means that apparent wind plays a very large part in the loads on the rig. Alternatively it does not take much sail area to move well. Many experienced slow boat sailors have passed a comment that the wind has dropped when, in fact, they have allowed the sails to luff or stall causing boat speed to reduce resulting in loss of apparent wind.  Similarly comments have been made that the wind dropped after turning off the wind and running or being alarmed at the strength of the wind when turning from a run to go upwind.  Dead downwind, a  HP will achieve boatspeed around 60% of windspeed without increasing sail area; apparent wind is very low. Sailing at 14kts downwind in 25kts of wind without any increase in sail area can be very deceptive as to the actual strength of the wind.  Doing 8kts or so on a slow heavy boat with the kite up in 25kts of wind is a completely different experience; there is no doubt about the strength of the wind under those conditions.  

Rick

On 13 Aug 2019, at 12:15 pm, StoneTool owly@ttc-cmc.net [harryproa] <harryproa@yahoogroups.com.au> wrote:

While asymmetry appeals to me at a gut level, I don't think anybody has 
really explained the reason for it on the HPs. Supposing the wetted 
portion the two hulls were identical, what effect would that have on 
performance and handling versus the shorter windward hull and longer 
leeward hull?   Presumably the slenderness ratio means less drag on the 
leeward hull...... It would seem that the fatter windward hull would 
benefit even more from length.

                                                            H.W.