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Old 20-09-2010, 22:12   #136
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I am not a big fan of diesels motors on boats.

I have had them and they are heavy & expensive and are not as reliable on boats as they are in Tractors and Trucks. The reason they are not as reliable seems that boat owners don't always run their motors under load (charging batteries etc) and this leads to glazing of the bore.
Also diesel motors don't seem to be properly marinized unlike modern day outboard motors.
They also put a diesel smell throughout the cabin
I also wanted to be able to lift the props clear of the water, so I can safely anchor very shallow or beach.

One other issue is resale value, if you are intending to buy a motor cruiser with Diesels, a great deal of the overall cost of the boat has been outlayed for the diesels and their installation. What if the motors are faulty which appears to be more often then not. You are up for a considerable amount of cash to replace them and this is reflected in the resale value when you try and sell.

I just purchased two 90 HP tohatsu outboards for $8,000 each.
Modern outboards are considerably more reliable than years ago, and after 200,000 hours I will replace them.

Finally,my concept boat is designed to go fast when necessary (15-17 knots) If you try and get those speeds with a diesel powered boat, the weight of the motor will go against you.

A displacement boat reguires 5 hp /ton (but you will only get displacement speed, which is the square root of the waterline length X1.34)
A planeing boat reguires a minimum of 60 hp/ton.

Fast displacement hull designs as used on commercial catamaran ferries and on my triangular hull trimaran design require 25hp/ton.

In regard to economy, which in the favour of diesels. I plan to sail as much as possible and use one 90 hp motor for a 9 knot cruising speed, and only use both motors only when needed
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Old 20-09-2010, 23:30   #137
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I am not a big fan of diesels motors on boats.


I just purchased two 90 HP tohatsu outboards for $8,000 each.
Modern outboards are considerably more reliable than years ago, and after 200,000 hours I will replace them.
Hi Beau, Just checking - do you really expect to get 200,000 hours from your 90 HP outboards or is that a typo?
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Old 21-09-2010, 03:47   #138
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I have been informed by commercial Oyster farmers in Australia that they get 200,000 hrs out of new generation outboard motors.
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Old 21-09-2010, 04:00   #139
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I have been informed by commercial Oyster farmers in Australia that they get 200,000 hrs out of new generation outboard motors.
That doesn't sound right - 200,000 hours is 22 YEARS non-stop (24 hours daily x 365 days per year).

Under normal operations, it would take the oyster farmers at least 66 years to confirm this type of longevity!!!! In other words, they'd just be scrapping a motor built in 1944.....
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Old 21-09-2010, 10:40   #140
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Re: motors

Beau,
Thanks for the detailed info on inboard vs. outboards. I agree with everything, plus an outboard is much easier and quicker to swap out if something happens to it. As you planned you basically have a main engine for low speed cruising and a backup if one ever goes down. Great info. Thanks.
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Old 21-09-2010, 12:46   #141
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I have been informed by commercial Oyster farmers in Australia that they get 200,000 hrs out of new generation outboard motors.
You have been grossly misinformed.
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Old 21-09-2010, 15:32   #142
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Ok guys it looks like i got the hours wrong, but they "oyster farmers" did tell me the new generation outboards are a lot better, I probably got too many "0's" in there.
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Old 21-09-2010, 15:54   #143
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Hey Beau,

Love the boat. I just finished reading the entire thread.

I was just wondering what your final length to width ratio is?

You mentioned 16:1 as the ratio to beat. But at 40ft long that would make you waterline width 2.5ft at the back.

Your plan images seem to put it at around 5:1.
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Old 21-09-2010, 17:38   #144
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For a fast displacement design there are currently two options. The 16-1 rule is for Catamarans and is mainly used on larger commercial ferries. There are a number of 40ft-50 ft power catamarans (Schionning)using this system.
The problem is the narrow hulls are not really suitable for accomodation in the hulls and they "hobbyhorse" a bit in shorter lengths.

I have developed a triangular hull design which has a very fine angle of entry which continues back all the way to the stern.
The very fine bow angle of entry negates any bow wave being formed allowing for much higher than displacement speeds.
The wide stern stops hobbyhorsing, this allows for fast displacement to be used in lengths under 40 ft.
The design is not suitable as a monohull because the narrow beam in this case 7ft 6inches for a hull length of 39 ft is relatively unstable. So I added outriggers.

My original version weighed in a 5 1/2 ton and the 2X 30 hp Honda outboards were too small. Top speed of 8 knots.

I have recently fitted 2 x 90 hp tohatsu outboards but i am still in the "running in" period plus I need finer pitch prop's.
I did achieve 12 knots with both motors running at 3,000 rpm and a very interesting 8 knots will one motor running at 3,000rpm. Max revs for these motors is 5,500rpm

An interesting thing happens as the boat reaches the 10 knot mark, the whole boat lifts up and the stern wave is significantly reduced.
It could be that the bow wave "is formed" but much further back lifting the whole boat (this was a comment by another CF member)
The boat is NOT planeing because the bow is further in the water than the stern (the boat has a flat bottom) No hydrodynamic lifting is involved as with a planeing hull. Plus I am using a lot less power. My calulations so far show a 25 hp /ton whereas a planeing boat needs 60hp / ton just to get up on the plane.
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Old 21-09-2010, 19:29   #145
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An interesting thing happens as the boat reaches the 10 knot mark, the whole boat lifts up and the stern wave is significantly reduced.
It could be that the bow wave "is formed" but much further back lifting the whole boat (this was a comment by another CF member)
The boat is NOT planeing because the bow is further in the water than the stern (the boat has a flat bottom) No hydrodynamic lifting is involved as with a planeing hull. Plus I am using a lot less power. My calulations so far show a 25 hp /ton whereas a planeing boat needs 60hp / ton just to get up on the plane.
I'd really like to see this in action because I am having trouble envisioning this phenomena. If the horizontal surfaces of your boat are flat...and it's powered from behind, by props that sit lower than the center of gravity of your boat...they WILL lift your bow and your boat WILL tend to plane (no matter how fine your bow is*). Now, your rule of thumb for a planing hull is probably based on calculations that involve the boat riding on top the water. I'm going to propose the idea that your boat could be sitting somewhere in between, partial displacement/plane as it were.

It is my guess that your boat might have some interesting dynamic quirks because it is a displacement hull with a fat square stern. To me, it seems like this could be a the source of a lot of drag and of lot of your boats inefficiencies. I noticed that in the original Trans-hydrosonic** (? I think was the term used in the triflection guys patent) hull that he had a deep narrow bow and a very wide stern that was EXTREMELY shallow.

*so long as it isn't so severely long and thin that its weight keeps it down while providing almost no lift.

**Transonic hydrofield and transonic hull...also see pg. 4 of his patent for hull pictures.
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Old 21-09-2010, 20:23   #146
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Power Trimeran "Earthrace" aka Ady Gill

What is everyones opinion on the power Trimeran "Earthrace" aka Ady Gill that made the fastest around the world trip? Cool looking design, but how functional is it to use a similar design as a live aboard?
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Old 21-09-2010, 20:39   #147
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I believe "Earthrace" was designed around a similiar concept that I am using, also Austal and Australian Company is building a number of navy ships for the US navy in Alabama I saw the scale model.
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Old 21-09-2010, 23:46   #148
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What is everyones opinion on the power Trimeran "Earthrace" aka Ady Gill that made the fastest around the world trip? Cool looking design, but how functional is it to use a similar design as a live aboard?
I was sad when it was hit by that whaling vessel and demolished.

I would say that the earthrace design would be a pretty poor live aboard...especially for a home builder. The major theme behind the design is the wave piercing hull which is extremely efficient in dealing with large swells. I would not want to live aboard a boat that tried to dive under water. You also need expensive things to make that safe (without your boat being too heavy for that hull design).

Another thing to consider is the speed you want to travel. Earthrace is optimized for something like 25 knots. If you want your live aboard to go that fast then...I hope you have serious cash. You'll find that at lower speeds the fine thin hull design doesn't net you such a big benefit compared to the loss of space.

Think about your car, then about a formula 1 racer. Putting the same racing grade suspension and spoiler on your car would be silly because it messes up the ride and doesn't really provide you with such great results in terms of performance. Same concept. The things earthrace were worried about in their design, most likely, simply will not matter in what you're planning (esp if its a sailboat).
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Old 22-09-2010, 07:03   #149
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Re: Earthrace

One thing that was interesting was that the boat could be submerged to something like 25ft as it pierced throught the waves. This would require some extensive engineering to prevent water from entering the engine intakes and exhaust as well as other hull fittings.
I watched a few episodes of Whale wars when they were on the Ady Gill and you are correct, the ride was extremely rough and the boat sacrificed space for speed. I'm still interested in a modified concept (toned down a bit) that is more suitable for live aboard but still has the stability of a trimeran and is more fuel efficient. Like most others I would plan my trips to avoid the bad weather but want a boat that can handle it and perform when needed. I would also prefer to build it with aluminum as Beau has done.
That's what's great about forums like this, we get to see all kinds of designs and talk with people who think "outside the box". My plan is to find out what I like from many different boats and then come up with an original design based on my needs and incorporate all the info into a platform that suits me. Plus I just love designing and creating new things.
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Old 22-09-2010, 12:06   #150
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One thing that was interesting was that the boat could be submerged to something like 25ft as it pierced throught the waves. This would require some extensive engineering to prevent water from entering the engine intakes and exhaust as well as other hull fittings.
I watched a few episodes of Whale wars when they were on the Ady Gill and you are correct, the ride was extremely rough and the boat sacrificed space for speed. I'm still interested in a modified concept (toned down a bit) that is more suitable for live aboard but still has the stability of a trimeran and is more fuel efficient. Like most others I would plan my trips to avoid the bad weather but want a boat that can handle it and perform when needed. I would also prefer to build it with aluminum as Beau has done.
That's what's great about forums like this, we get to see all kinds of designs and talk with people who think "outside the box". My plan is to find out what I like from many different boats and then come up with an original design based on my needs and incorporate all the info into a platform that suits me. Plus I just love designing and creating new things.
Excellent mentality. Just make sure if you have a HIGHLY skilled professional boat designer give your idea's a once over if you try to build a submersible. Building a general approximation, tapping on the side and calling it sturdy...could lead to disaster.

I'd also say the "extensive engineering" would have to be around hull design. The whole...dealing with water ingress...is the easy part. If you look up the system on earthrace it's pretty simple.

I have to ask...if you are planning on avoiding bad weather. Why consider a wave-piercer at all?
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