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Old 12-16-2013, 09:13 AM   #181
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DSe Sunshine's Aft Sections

Parmenter -

Here are two CGI images of Sunshine with her "as-designed" aft sections (ignore the size of props and rudders - the artist missed a bit on both - but the lines are a good reflection on the design). We used semi-circular sections leading aft from wave-piercing bow then tapered conically to the propeller aperture (not unlike a torpedo). At the point where we start this taper, the chine continues aft with a flat section to the trailing edge of the transoms.

Even though this image shows bottom paint on these flat sections, they were intended to be above the waterline at slower, displacement speeds - immersing into the water only at higher speeds. Initial sea trials in Zhuhai showed this to be the case as were tank tests in Shanghai. The photo of sea trials shows a bit of immersion aft at displacement speed.

We did not install enough power originally to get much beyond 9 knots - power was serial hybrid from Glacier Bay, each motor measuring maximum of 18 kW (instead of the advertised 25 kW).

We ended up installing parallel hybrid with ZF sail drive from Steyr 75 HP diesels/7 kW electric motors. We needed to reconfigure the trailing section of the bottom to accommodate these legs - not as pretty as original concept. Also, we ended up adding significant weight (diesels aft along with lots of wood and structure), so the flat sections aft were immersed along with the chine and some "ugly" sections above the chine. Top speed with these diesels remained at 9 knots.

I have also attached an "as built" photo showing the aft sections as modified for the sail drive leg. My guess is that this treatment is not unlike the aft sections of other displacement power cats - the flat sections are now well immersed (as indicated by the bottom paint). If we had more HP, I'm sure we'd break the 9 knot barrier and reach speeds in the low teens - unfortunately, our decision to use sail drive precludes more HP as they are limited.
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Old 12-16-2013, 12:00 PM   #182
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jtrane,
I actually kinda like it now that I've been exposed to the hulls below the WL for a few days. Looks very efficient indeed and very flexible in her speed range. Another benefit of high aspect ratio hulls that can be maximized w the cat configuration.
When quartering seas do cats have a tendency to stick their props out into the air?
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Old 12-16-2013, 01:31 PM   #183
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CS Hull Form

Another view of what Tennant referred to as the CS hull form (canoed stern)
[PCW] CS hull form

Malcolm Tennant Multihull Design Ltd - About


...here is a good article of his, with some photos of just some of the vessels that made use of this hull design
Multihulls
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Old 12-16-2013, 01:40 PM   #184
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Another benefit of high aspect ratio hulls that can be maximized w the cat configuration.

What's that mean?
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Old 12-16-2013, 02:14 PM   #185
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Length/beam ratio?

Never had a prop cavitate in any conditions.
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Old 12-16-2013, 02:35 PM   #186
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Length/beam ratio?
Yeah, of a single hull at that probably. Should'a just said so instead of making up new terms. Way to much of that already.
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Old 12-16-2013, 02:38 PM   #187
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......

We ended up installing parallel hybrid with ZF sail drive from Steyr 75 HP diesels/7 kW electric motors. We needed to reconfigure the trailing section of the bottom to accommodate these legs - not as pretty as original concept. Also, we ended up adding significant weight (diesels aft along with lots of wood and structure), so the flat sections aft were immersed along with the chine and some "ugly" sections above the chine. Top speed with these diesels remained at 9 knots.

I have also attached an "as built" photo showing the aft sections as modified for the sail drive leg. My guess is that this treatment is not unlike the aft sections of other displacement power cats - the flat sections are now well immersed (as indicated by the bottom paint). If we had more HP, I'm sure we'd break the 9 knot barrier and reach speeds in the low teens - unfortunately, our decision to use sail drive precludes more HP as they are limited.
I proposed a gamefishing-motorsailing cat, and utilized a slightly modified Tennant CS hull form with out-drive-legs.

But as I was intending to use greater HP on the motors I abandoned the conventional 90-degree drive legs for a 'parallel' drive arrangement utilizing silent chain/belts,.....not just a single belt but rather a dual arrangement that would accommodate counter-rotating props.
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Tennant Hull V ChainDrive

Chain Drive
YachtForums.Com - View Single Post - New Drive System from Volvo Penta
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Old 12-16-2013, 03:41 PM   #188
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Pacific Harmony

Another big power cat that utilized the CS hull form, albeit modified the bows a little bit....
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Old 12-16-2013, 06:51 PM   #189
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Brian. Did you ever build the cat with counter rotating props driven by belts? I love that idea! Was the engineering done on the shafts ?

If course , you can get up to 350 HP Volvo with a stern drive. We used these - twins - in our 42' monohulls - the Island Pilot 395. Speeds in excess of 30 knots on a 32,000 boat.
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Old 12-16-2013, 09:14 PM   #190
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Belt Drive, Chain Drive

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Brian. Did you ever build the cat with counter rotating props driven by belts? I love that idea! Was the engineering done on the shafts ?
I did not get that built, nor did we go forward with the 'belt drive' concept. There was no development monies available.

I had started out thinking Kevlar belts, but became convinced that the silent chain was a better idea. Here is a posting (2004) where I was going thru that transition:
YachtForums.Com - View Single Post - New Drive System from Volvo Penta

PYI had come out with a chain drive leg, but only marketed it for a few years. I'll see if I have a few other photos of it. I did collect a lot of info on these silent chains and identified a prime manufacturer I wished to work with on development of such an outdrive leg,...if some development monies should become available.


One sample installation I saved on my older computer
Paradise 60 :: Paradise Yachts

One older spec sheet on the smaller sized unit:
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Old 12-16-2013, 09:48 PM   #191
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Rick and trane,
Length to beam ratio = long skinny hull has big numbers like 5-1 ... The favorite of Atkins or 3-1 = fat and wide.

High aspect ratio hulls like cats, canoes and kayaks can easily break the hull speed barrier. I have a powered canoe that goes faster than my 30' trawler. So they are not so limited and have much greater flexibility from a standpoint of speed range.
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Old 12-16-2013, 09:56 PM   #192
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Parmenter that craft looks a bit like the new Integrity 440 side onů
I thought so too. Like cutting down the centre, with cat stuff in between.
Benn, Kevin Dick`s Kellick 33 always attracted me, nice no nonsense boat, a modern(ish) Masters 34.
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Old 12-16-2013, 10:00 PM   #193
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The cat from Georgetown, SC. I would think she's one of Tennants designs?
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Old 12-16-2013, 10:20 PM   #194
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A very nice artistic rendering of another Tennant design. just ran across this in my older files while searching for the drive info.
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Old 12-16-2013, 10:45 PM   #195
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Isn't that Domino?
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Old 12-16-2013, 11:25 PM   #196
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Isn't that Domino?
Sure is
http://www.hallmarinedesign.com/2_ma...ower-catamaran
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Old 12-17-2013, 12:33 AM   #197
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Wanted to share a sail cat turned power story about friends boat...
Started life as Viva sailing cat and then he sold rig and built lightweight pod cabin house and added the reverse bow design. Boat is 30ft? powered by twin 15HP. Cruises at 15knots and tops out at 18knots and gets "claimed 8 to 10 MPG" at cruise speed. It does so using the existing non modified sailing cat hulls and experiences no squatting up to 18 knots. Have a look at profile and hull shape. This is probably the 20th boat he has built.
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Old 12-17-2013, 06:56 AM   #198
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The nature of the fly bridge on that latest rendering could be adapted to the M52 enhancing her looks.

Brian. Thanks for all the info you've listed. Really enlightening.
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Old 12-17-2013, 03:13 PM   #199
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M52
I like the Viva a lot. And I could USE that boat. I usually don't like the looks of cats but I even like it's looks.

I'm wondering about his other 20 boats?

I'm not nuts about fly bridges on mono hulls but as long as it's light they should work very well on cats. Also because of the shape of their hulls the FB windage shouldn't effect them much either. Hadn't thought about that before but usually don't think about cats. One of the benefits of forums is that you get exposed to things you would normally skirt around and not notice.

Thanks
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Old 12-17-2013, 03:48 PM   #200
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M52
I'm not nuts about fly bridges on mono hulls but as long as it's light they should work very well on cats. Also because of the shape of their hulls the FB windage shouldn't effect them much either. Hadn't thought about that before but usually don't think about cats. One of the benefits of forums is that you get exposed to things you would normally skirt around and not notice.
Keep this in mind.

Have you ever been up a mast on a sailboat, or up in the tuna tower of a sportfish. The motion of the vessel gets a little exaggerated up there.

Now make it a multihull and that beam motion can become a lot more 'instantaneous', ....jerky ....fast elevator ride-ish
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