Designing a fast open deck catamaran

All weather docking station will be cool feature .

I am not a sailor, so even on a 7.5m minicat I plan to use 2 small engines. Redundancy and maybe a little more "power".
They will be a bit heavy but maybe I will make a light boat.

The idea of using a tender as the main engine on a 15m boat is rather dangerous.A lot of situations can go wrong.

You can use aluminum or hdpe tender with some fenders. Inflatables they have their own problems sometimes.

 

I think idea to use tender to also to drive main boat is kinda neat. Just not sure how it would cope with steep waves while attached to main boat bouncing up and down. In theory it is similar to sled mounted outboard, but outboard sleds are much smaller and don't float the outboard end.
It embraces the KISS principle. Only one engine to maintain and powerful tender. If numbers are right then Harryproas are super light boats 15 m C50 is supposed to weigh only 2 tons empty, 4 tons fully loaded. A regular 25 hp outboard should drive it just fine. Although don't expect to overpower high winds with it. Sails give redundancy and extra power to fight strong winds. Every regular monohull sailboat has one engine and seem to get by just fine. Modern fuel injected outboards are very reliable and unlikely to randomly fail if maintained properly.

 

The tender has a multi-hull stern, maybe the floats will hit the water less than e.g. a mono tender.

Let's say so.

I don't agree.

Yes they are . What if you lose the engine ? New 4 strokes also have disadvantages for me.

 

Possibly, but that is something I would really like to see in action before committing building such unusual system.

I think for sailboat risk is acceptable, there even are plenty of single engine powerboats that go offshore and they don't break down and need towing all the time. Sailboats have built in redundancy in their sails. I would better invest my effort and money in making sure my rig don't break than into second engine. If adding second engine I would probably add some sort of oversized electric trolling motor for short range silent slow speed cruising and better marina maneuvering. Big battery bank have plenty on non propulsion uses too on live aboard cruiser.

They are more complex and heavier, but now 4 strokes is all there is. New two strokes are no longer sold in EU. 4 stroke outboards are common all over the world used on local boats, plenty of people who know how to fix them and parts no too difficult to find. In this regard outboards are better then diesel engines that often have highly custom parts.

 

I am new to sailing and I see things with my own eyes.
I often see sailboats as dangerous, cheaply made, heavy, poorly engineered. There are some exceptions.
More engines always better.
Big battery bank ok . For better marina maneuvering some thrusters maybe . But decent sailors don't need them.

 

Most production boats are made to a price point. Average sailboat is parked in the marina most of the time and go out on weekends when weather is nice with occasional longer trips thrown in. They are mostly good enough for that purpose. Special purpose built expedition boats are much more heavy duty and as a result cost 2x to 3x more.

 

You sailed quite far .
The word expedition has a different meaning nowadays.

 

Hulls, beams and various bits of weird experimental rigs are built, I have PM'ed you his contact details. He also has an 8m version which is semi finished.

We chose the standard width for a good combination of righting moment, windage, beam twisting, acceptability and ww hull drag post shunt (not an issue with the schooner rig). The space in the ends is pretty useless and storage there encourages pitching. It can be as long as you like, as long as the waterline l/b ratio doesn't exceed 11. A shunting cruising catamaran (ie, equal hull length proa) makes more sense than a tacking/gybing one.

My 7.5m schooner rigged test bed went upwind well. Best example was starting behind and to lee of a 49'er in an Olympics campaign. Passed him to windward, gybed, went back and did it again.

Perhaps. It is all about sail/rig trim, much the same as for a jib/mainsail rig.

No idea of upwind vmg (too many variables), but tacking through 90 degrees is normal on all the boats so far. Max wind would be very high as schooner rigged shunting boats do not need to maintain speed to tack and ensure steerage. Standard is an 80% reef which should be good for any wind it is sensible to sail in. Sea state limits are more about steepness than size and have as much to do with your steering ability as the boat. I would have raised the boards, dropped the sails and gone inside for a cuppa before either was a problem. Perhaps dropping a parachute anchor if I did not want to lose distance. This is far easier to do working from the cockpit on a double ended proa, than over the bow on a conventional boat.

The ss pin for the rudder pintles needs holes drilled in them, everything else is composite. The hatches are included in the infusion, there are no metal fastenings in the construction.
On my latest test bed (24m, 3 ton cargo proa) the mooring cleats are composite and, along with the winches, attached with carbon tow. Look through the updates for photos of details

The board is also supported at the bottom of the case. It's an engineering issue. There is more than enough carbon to withstand the loads.

The rudder plates are in a case so they can be raised. This case is attached to a drum in the hull which rotates in an impact.
The next leeway/steering arrangement on the cargo proa is the simplest of any boat, except those steered with a paddle.

They are light, but less weight sensitive than a cat, tri or mono. You can load the lee hull as much as you like. The boat will go slower, but the loads on the masts and beams will stay the same.
In ply, it would take longer to build, need more maintenance and be a bit slower or have less payload, none of which are insurmountable problems. The beams, rudders, masts and booms should be composite as they have a fair bit of carbon in them. Infusing them keeps the cost and weight down and the quality high. Wood would not be suitable.

800mm at the waterline, 1.2m would be ok. Performance will suffer a lot at 1.5m or wider.
The deck is 1.2, could be as wide as you like. One owner has put on a full width bridge deck cabin, another intends to add bunks on the inside of the hull between the beams.

Docking the tender in 1m seas would be a challenge. I'd have a docking station on the outside of the beams as well as the inside. Hook the boat up and push from behind. Hooking up and docking are simple. The tender in the normal position is clear of the beams so can go up and down as much as required when docked. The C50 is a boat for sailors. The motor arrangement is not perfect, but saves a lot of weight, smell, cost, space and in cabin heat.
The tender is huge, with all the attendant advantages and disadvantages. A small tender for crowded docks, carrying up the beach (and boarding in 1m waves ;-)) would be a good call if these were regular occurrences.
The cargo proa has a 6 kw electric pod motor on the end of a rotatable tube through the toy box. Easily lifted/deployed, it allows thrust in any direction and can be used as a hydrogenerator.[/QUOTE]

 

Thanks

Interesting, tacking and gybing have never bothered me much. With self tacking jib tacking upwind in normal cat or mono is super easy, you just push the tiller over and that's it. Less work than shunting where masts need to be rotated and booms pulled in when reversing on opposite tack. It takes more effort if you have extra large headsails that need to be tacked manually or gybing gennakers downwind, but still pretty manageable even alone. I think where Harryproa rig really shine is ease of depowering when sailing fast downwind and getting caught in rapidly raising wind situation. A normal mainsail if released would just slam in stays and not depower. To get it down would require turning into wind which would briefly power the sail up even more increasing chance of capsize.

I was more concerned about situation where you MUST make progress upwind or you crash like getting caught in a unforecasted squall pushing toward rocky shore, where waiting it out on para anchor not an option.

So essentially better all composite and not mix and match different materials.

That's good to hear, I think something like 1 - 1.1 m at waterline and 1.6 - 1.8 m at shoulder height would be nice. I would like to have a big work table (about 0.8 x 2 m) in space between masts. The leeward hull as shown in renders is too narrow to fit it. Work table also could have secondary function as a bunk if needed. A bit wider hull at waterline would also give a little more load capacity. I look at it in a way that leeward hull is big part taking large fraction of materials, cost and time so may as well build it in a way it is really usable.

I see that. I would probably opt for main outboard on sled like used on most outboard powered catamarans and have another small outboard for lightweight tender. I want my tender be light enough so I can drag it alone above high tide level on a rocky beach. A 6 m composite tender with 25 hp outboard far too heavy and fragile. A small lightweight inflatable boat with transom for little outboard probably best for this application.

Do you have any idea when first C50 or C60 will be sailing. I would really really love to see some videos of it sailing in various weather conditions, especially in rough water. So far various videos I managed to find of earlier Harryproa versions were only in flat water easy sailing conditions where any performance boat would sail well. So far it seems that everything should work, but I still have little bit of doubt that there could be some unforseen problems. It is still fairly experimental at this stage.

 

Correct. Hoisting, lowering and reefing sails on any point of sail, in any wind strength and the ability to depower instantly and completely are huge advantages of unstayed rigs for cruising boats. As is the ability to fit a simple, near idiot proof anti capsize fuse activated when the windward hull leaves the water either sideways or fore and aft.

This is far easier in a shunter than a tacker for the reasons given in my last reply. Not having to be overpowered to enable tacking, or worry about getting into irons makes it much less stressful. It doesn't work on rocky shores, but an alternative to bashing upwind off a lee shore that is sand or mud is to sit the boat on the beach. The low draft (2-300mm on the C50) means the boat sits above the zone where waves do damage. It gets gently washed up as the tide comes in, is halted by the anchor just before high tide, sits high and dry during the storm, then is easily relaunched when conditions allow. I discovered this inadvertently when an early version broke it's mooring in a gale and washed up on the beach (3,000 mile fetch). The next day it was high and dry and undamaged. A bunch of us pushed it down the beach and sailed it home.

No problem mixing wood and composites, but metal on a boat apart from where you need weight, heat or wear resistance is generally a stress raiser, potential leak and requires beefing up to spread the loads.

No problem.

Sleds work, we put them on the early designs.

Not really. The one we are building here could be first, although 'island time' and other projects could get in the way. The C60 in Peru is back under construction, should be finished this year. The C50 in Australia is currently closest, but it is a one man band.

So would I! This is one of the reasons we are building one.

No video, but an overloaded 12m crossed the Tasman a few years ago. Hove to for a day in 45+ knots, broke a ring frame which should have been a bulkhead but otherwise was a delight to sail, according to the owner.[/QUOTE]

 

Rob, you mention "as long as the l/b doesn't exceed 11 - 1"
Why do you say that ?
Is the lee hull 11/1 ?

 

I have never sailed a proa. But imagining sailing her upwind, both hulls entering the wave at the same time and moving together ... Compared to a cat with two hulls of equal length, each trying to impose its movement on the other, it looks for me like a much smoother ride, with much less stress on the structure and crew. Thinking this is a main advantage of a proa, I am curious if experienced proa sailors agree.

On the other hand - in light winds and low speeds when frictional drag dominates, the shorter luv hull produces LESS drag because its wetted surface is smaller in relation to displacement. As the wind and the speed are increasing, the weight is transferred more and more to the slender leeward hull, which causes less wave drag ... it looks very unusual and I don't know how it works in practice, but from a technical point of view this is a very elegant principle.

 

It occoured to me that motoring and motorsailing is possible only in one direrction. I wonder if it is feasible to center both sails and motorsail by tacking. I often do this with my 9.5 m sailing cat in a river where wind often is too inconsistent to reliably sail. Leave the mainsail up and centered and motor. When a gust hits fall off a bit and let mainsail power up and provide extra drive to cancel out wind drag against the structure. Doing this with shunting in narrow river would be very tedious. Sometimes headwinds in narrow channel can be too strong and owerpower a small outboard, but not enough space to reliably tack upwind under sail alone. Then motorsailing and tacking with mainsail pulled tight centered is only way to get upwind in narrow channel. Motor+mainsail tacking works well even if tacks are very short like only 20 - 30 meters. Could you also tack a proa this way if required? Would it cause some issues if leeward hull becomes windward hull in fairly calm water, but strong wind?

That's good to hear. I wonder how high are the beams above water. Performance catamarans of this size generally have about 1 m clearance to avoid excessive slamming. Forward beam often about 1.5 m above water level to prevent it striking water and becoming huge drag. In renders C50 looks lower. I wonder with hulls being narrow with little bouyancy at the ends could there be a an issue with beams slamming into waves. In some of the videos I saw with maybe about 0,5 - 0.7 m waves the rudder/board assembly started to strike waves and threw a lot of spray causing extra drag and it looked like crossbeam also are not far from striking wave tops. How would C50 behave in 1,5 - 2 m steep waves sailed hard at various angles . If going fast downwind could front beam strike water if bows burry a bit in a wave in front increasing risk of pitchpole.

It would work with wind and waves same direction, but that often is not the case especially near capes and islands and when wind direction shifts rapidly so the boat has to be able to handle that.

That sounds good in theory. I wonder how it works out when both hulls produce different levels of drag force. Would boat try to turn towards more draggy hull and have to be compensated by slight rudder deflection?

 

Reefing how to do it ?

 

Return of the Jedi ? :