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Old 16-05-2011, 18:46   #181
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Re: Beau's Boat

Would you say the concept has worked? Originally you said it would be capable of CRUISING at 10 knots on one 30 hp motor, and 20 knots on two of them.

Now you are cruising at 7-8 with bigger (and thirstier) motors. To be honest your fuel use seems heavy to me. My own boat is much more economical, using around 1/3 of the fuel motoring at similar speeds, and it is also carrying a fully functioning sailing rig (which adds considerable weight and windage when motoring) - that enables it to sail to windward as well as downwind.
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Old 16-05-2011, 18:58   #182
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Re: Beau's Boat

As I have said earlier the boat is a work in progress.
With two 90 hp tohatsu's I can do 17 knots but use considerable fuel.
The design was built by professional boat builders and came in at twice the estimated weight.(plus liveaboard items)
I am still working on the fuel consumption bit, however I chose petrol outboards because they are much lighter and considerably cheaper than diesels and the props could be lifted clear of the water when I beach, which is often.
I intend to motor sail most of the time for economic reasons.
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Old 17-05-2011, 20:28   #183
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Quote:
Originally Posted by beau
Gordmay
It is not that simple.
As I said earlier there are two factors at work with speed and "overloaded" multihulls. Increased Wetted surface and Bow wave formation.
The friction formed with wetted surface is linear and follows the principle of "to double your speed reguires four times the power"

The drag caused by bow wave formation jumps 10 times as you get beyond displacement speed.
What I am suggesting is, it is the dramatic change in hull form in mutihulls when overloaded that causes a dramatic increase in drag caused by bow wave formation at speed, and not so much wetted surface drag.

With this knowledge it is possible to design multihulls that "can" carry extra weight which has little affect on performance other than the "small" increase in drag caused by extra wetted surface.


I was re-reading this thread with interest, as someone who has built a few boats (ok dinghies) but is really interested in the theories you mentioned. The main flaw in your argument is assuming that with flat sides, you are only increasing wetted surface drag when the boat is loaded. You are going to submerge the boat deeper if the hulls do not flare, and will still have to move the increased water displacement as well which creates drag, regardless of bow wave formation or not. Displacement is still displacement, and you can't fool the water, as Archimedes discovered. Easy to armchair quarterback, having read the end of the thread... but regardless of the design, weight greatly affects your ability to exceed hull speed.
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Old 18-07-2011, 22:19   #184
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Re: Beau's Boat

Update,
Currently at Hope island (cooktown) waiting for a weather window, it is currently blowing 30 knots SE.
Finally got our CAIT for Indonesia and a six month visa.
The boat has performed well in 25 knot SE winds motoring downwind.
I just love the shallow draft (18 inches)
The DIY watermaker using a 6.5hp gasoline pressure washer works well and produces 150 litres and hour
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Old 19-07-2011, 07:33   #185
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Interesting Adventure, from building thru cruising

Best of luck Beau with your adventure. And please keep your postings coming.

I've made reference to this subject thread over on Boatdesign.net that should bring you some additional followers.
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Old 19-07-2011, 07:34   #186
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Homemade Watermaker?

Quote:
Originally Posted by beau View Post
The DIY watermaker using a 6.5hp gasoline pressure washer works well and produces 150 litres and hour
That's interesting...would like to hear more
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Old 19-07-2011, 08:43   #187
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Re: Beau's Boat

Quote:
Originally Posted by beau View Post
Update,
Currently at Hope island (cooktown) waiting for a weather window, it is currently blowing 30 knots SE.
Finally got our CAIT for Indonesia and a six month visa.
The boat has performed well in 25 knot SE winds motoring downwind.
I just love the shallow draft (18 inches)
The DIY watermaker using a 6.5hp gasoline pressure washer works well and produces 150 litres and hour
Whatever happened to the much talked about crab-claw sails? IE, why are you motoring downwind?

Jim
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Old 19-07-2011, 20:42   #188
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Re: Beau's Boat

desalinator- brett swain recommends 3 gallons a min salt water feed which gives 1 gallon a minute fresh water and a 2 gallon flush. For a flow rate of 3 gallons a minute a pressure washer needs to be a 6.5 hp gasoline unit.
I flush with fresh water after each use.

Sailing - I have an inexperienced female crew and sailing downwind in 30 knots is not the time to train her.
Also we need to reach TI fairly soon, and motoring at 8-10 knots is faster than sailing.
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Old 11-08-2011, 16:31   #189
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Re: Beau's Boat

We are currently at Thursday Island the tip of australia, we left Brisbane 4 months ago winds were 20-30 knots SE most days. we found it best to leave at dawn and travel short distances 30 nautical miles to the next island before lunch.
The shallow draft made cruising more pleasant, we could get in close to the beach and avoid most of the swell.
The DIY desalinator has been fantastic, simple to operate and 150 litres of fresh water an hour made life more comfortable. Thank you brent swain for your help. No bells and whistles just a petrol pressure washer and 2x 40 " pressure membranes and simple plumbing.
We lost one solar panel in a gale, so we are waiting at TI for a new one to be flown in. I threw the Kipor generator overboard and bought a 2kva Honda. It is so much better. (don't buy a Kipor)
The tohatsu 90 hp two stroke outboards have been excellent. It is great to be able to lift them clear when beaching.
I normally run them at 2,000 rev's each for a speed of 7 knots at 3 litres a nautical mile.
We haven't done much sailing yet, because we seemed to always get 30 knots or 5 knots of wind. However that will change once we get into Indonesian waters
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Old 13-08-2011, 08:28   #190
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I am very jealous! Looks like you're having a great time. Now that you have had time to extensively seatrial , do you think it really is possihke to build a full size cruiser like your lightweight enough to get the performance you had envisioned? It seems once you load up for cruising with long range fuel tankage, furnishings and equipment, the weight was going to come in too high to match your plywood prototypes.
Really interested by the physics of your boat, even if the performance and economy didn't pan out as you thought. But your shallow draft and easy to manage power plants seem like a great asset even if you cruise at only 7 knots.
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Old 13-08-2011, 16:15   #191
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Re: Beau's Boat

With the two 90 hp tohatsu motors at max rev's the boat will do 17 knots. however we use a lot of fuel, which is ok if you are only going a short distance.
We now weigh 7 ton, to power a planeing boat at this size and weight you would need at least 400 hp.
My latest addition is a 10 hp fourstroke outboard which use's a max of 2.5 litres an hour and pushes the boat at 4.5 knots for long distance travel.

With the fine bow entry the boat handles 25 knot conditions very well.The boat is very stable particularly at anchor, with no rolling, but we do try and get in close where ever possible.
Having just come up the east coast at the worst time of the year, 20-30 knot winds, i believe we had a much better time of it than other sailing monohulls we are sort of travelling with. When the weather gets really bad they shelter just like us, but when the weather drops off (calm) they have no wind to sail.
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Old 11-11-2011, 17:59   #192
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Re: Beau's Boat

Currently in Fakfak, Irian Jaya,
This is not a place for cruising boats, the water is shallow, and there is no wind.
We have a shallow draft trimaran and outboard powered, fuel is cheap.
Spare parts are impossible to get, we had to fly to Australia (darwin) to pick up new charts and an Inverter.
We are now heading towards Ternate and Sabah Malaysia.
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Old 07-04-2012, 19:07   #193
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Re: Beau's Boat

Currently in Menado Sulawesi Indonesia.
We left Brisbane 1 year ago, cruising up the QLD coast to Thursday Island. Our first overseas port was Merauke, Irian Jaya. It is possible to check in there but not recommended.
We cruised along the southern coast of West Papua, water was very shallow, mud and little or no wind. Natives are OK but not very friendly.
At Kaimana the water was clearer, blue and the coastline beautiful limestone.
Nobody speaks any English here, so communication is difficult. Internet is also poor.
Everthing is very cheap but there is very little to buy.

After leaving Sorong we entered Indonesia proper, which was better, people very friendly, no meat to buy,and buying fuel was difficult.
We got as far as Bitung/Menado and were informed that my Pension was suspended because the Australian government had changed the rules and now required that we live permantly in Australia.
We decided to come home so we put the boat into a 40 ft container and have sent it to Brisbane (cost US $4,000) see attachments.
I will supply more information over the next few weeks, any questions please ask.
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Old 07-04-2012, 19:54   #194
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Re: Beau's Boat

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and were informed that my Pension was suspended because the Australian government had changed the rules and now required that we live permantly in Australia.
That absolutely sucks Beau.
Can you provide a link to this change in legislation?
It will be knocking a lot of peoples plans on the head I would think.
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Old 07-04-2012, 20:04   #195
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Re: Beau's Boat

Sorry Dave I don't have a link, just go to centrelink.
My payments were cut off without notice. I flew back to Darwin to sort it out and was told of the "new" rules for disability pensions, I do not know about other pensions.
It definitely stuffed up my plans, pretty rude if you ask me, but I was told (with a smirk on the face of centrelink staff) that there was nothing I could do about it.
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