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Old 09-29-2019, 01:11 PM   #81
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From the Selene website, under "Yachts/The Selene Advantage:"
The design incorporates the fuel efficiency of a full-displacement hull. A full-displacement hull is designed to remain fully in the water throughout its entire range of speed. This requires a fraction of the horsepower that semi-displacement or planing hull requires to attain optimum speed. A full-displacement hull will be capable of maintaining speeds in the 7- to l2-knot range while burning a minimum of fuel.
Didn't look at individual model descriptions...

-Chris
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Old 09-29-2019, 05:04 PM   #82
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Quote:
Originally Posted by Nomad Willy View Post
syjos wrote;
“Are Selens full displacement?

I thought they were semi.”

The one in post #59 is not even close to FD. SD to be sure.
The GH in #69 is clearly FD.
The one above in #70 is also SD....
IMO

The Seaton above has a very interesting fore and aft support for the lower shoe. Never seen that before. Probably too much drag for much in the way of SD speeds. But w props that far inbd. she probably runs straighter than most running one engine.
Not sure whether displacement or semi-displacement. Best I can tell from photos the QBBL angle is around 6 degrees. Regardless, there will be no semi-displacement speeds for us. With 50' LWL and 300 hp to push 45 tons we cruise 6-7 knots, topping out around 10 knots.
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Old 09-29-2019, 05:47 PM   #83
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DCDC,
I started another thread on FD/SD.
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Old 09-29-2019, 05:50 PM   #84
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Quote:
Originally Posted by Nomad Willy View Post
Captian SEA,
Speeds or speeds attainable is not an identifying element of FD/SD definition.
It’s all about hullform. If you don’t at least have some QBBL angle aft the hull is either planing or SD. Not ever FD.
I don’t follow Nordhavns. Show me a pic of their stern below the WL and I’ll comment. In a new thread. This is not on topic.
Hi,
Your answer regarding not following Nordhavn tells me all....

Thank you anyway for your contribution.
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Old 09-29-2019, 05:58 PM   #85
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Quote:
Originally Posted by ranger42c View Post
From the Selene website, under "Yachts/The Selene Advantage:"
The design incorporates the fuel efficiency of a full-displacement hull. A full-displacement hull is designed to remain fully in the water throughout its entire range of speed. This requires a fraction of the horsepower that semi-displacement or planing hull requires to attain optimum speed. A full-displacement hull will be capable of maintaining speeds in the 7- to l2-knot range while burning a minimum of fuel.
Didn't look at individual model descriptions...

-Chris
Thanks for your post, in fact just making a quick surch on the net and it will become clear that Selene are FD, unless the articles and reviews from Passagemaker and the like are all fake!!! I am sure that Howard Shen, the world renowned Naval Architect and owner of Jet Tern Marine (Selene Brand) would be happy to learn that according to a TF member, his designs are not what he thinks, I will send him a quick note today to let him know...
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Old 09-29-2019, 05:59 PM   #86
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CaptainSEA,
I started another thread for you to address your concerns.
Called SD/FD and I’ll transfer your post here over there.
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Old 09-29-2019, 06:12 PM   #87
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It's all personal preference. Each of us values pros and cons differently.

Single props and rudders are better protected, but my first twin was 1961 and I never damaged a prop. I operate in log country and more recently Japanese tsunami debris. I have purposely grounded, carefully on mud and sand banks for various reasons and sometimes by accident. But the bow grounds long before the props are in range of the bottom. When a friend was on watch, hit a big log in Canada in my current boat without damage. I have a monel plate on the bow. No damage to the bow or props.
The fuel savings is not that great for a single. And a single can be a handicap if you operate in places with strong currents. My boat on one engine goes less than half the speed with two and that's freewheeling the prop.

With twins, in remote places, you can make repairs between parts of the two engines to get one running.

I have a day tank and feed all mains and generators from that. And that's the setup I usually have in all boats/ships I've owned, built or operated for others. I've never had a bad fuel problem in 58 years of running my own boats. Those that have should maybe question their methods and maintenance.



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Old 09-29-2019, 06:43 PM   #88
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Seems you're a good experienced skipper who can make about any drive train setup work quite satisfactorily. Good post.
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Old 09-29-2019, 07:38 PM   #89
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Quote:
Originally Posted by Nomad Willy View Post
The GH in #69 is clearly FD.
Willy, can you explain why post 69 is FD. I read the brochure on it and it says FD, but any description of FD says rounded bottom.
Looking to learn something.
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Old 09-30-2019, 11:33 AM   #90
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Quote:
Originally Posted by Soo-Valley View Post
Know your boat.
Unless there was a 'V' in a reef that I threaded the keel into the props are protected as the forward part of the keel would hit first. Sure run aground and have the tide drop. lean over prop shaft damage. Sure run over a water logged object and it may take out one of the shafts. A lot must all conspire against you. But please stop saying props are unprotected suggesting imminent damage awaiting.

Attachment 94547
This exactly. We spend most of our boating time in the Bahamas and Florida. I've run hard aground twice and bumped many many times. It's the price of entry where we go. I only did prop damage once and I would have damaged a single then as well.

The keel is lower than the props and rudders.
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Old 09-30-2019, 11:51 AM   #91
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Quote:
Originally Posted by Soo-Valley View Post
Willy, can you explain why post 69 is FD. I read the brochure on it and it says FD, but any description of FD says rounded bottom.
Looking to learn something.
By rounded bottom you mean soft chines?
The only roundness the leads to FD is the shape of the stern on the bottom of the boat. From 1/3 to 1/2 way fwd from the transom. As in this rowboat example. See that the bottom “rounds up” to the transom and the transom is usually out of the water even when loaded. It’s all about the bottom aft of amidships. It can be a flat bottom, V bottom or a rounded soft chine bottom.

Most associate a soft chine with a slow boat and transfer slow and round to FD. It’s a bit of a trap. Also FD boats can have any number of chines. Some stitch and glue constructed boat have 3-4 chines. Usually a substitute for a round chine/bottom.
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Old 09-30-2019, 12:03 PM   #92
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Quote:
Originally Posted by Soo-Valley View Post
Willy, can you explain why post 69 is FD. I read the brochure on it and it says FD, but any description of FD says rounded bottom.
Looking to learn something.
Yes,
The water line rises in the stern to the end of the boat (transom). Go to the thread FD/Sd and see the pic of the rowboat w a FD stern. The rise in the stern is obvious and even profound.
This FD/SD chat should be on the new thread specifically for that to quit the off topic content.
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Old 10-04-2019, 01:21 PM   #93
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There's always the third solution, for those with the necessary funds. Check this one out with a 70hp Daewoo auxiliary engine with its own dedicated propeller shaft:

https://www.passagemaker.com/cruiser...ing-class-hero

https://images.atlanticyachtandship....isces-full.jpg
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Old 10-04-2019, 01:40 PM   #94
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I like the twins for redundancy and manouverability. Some transmissions allow freewheeling which means you can run on one engine with the other turned off. I do this often when running at displacement speed on my Mainship 43 with ZF transmissions. The fuel burn is about the same because of the added drag of the freewheeling prop but the maintenance costs are halved. Best of both worlds with twins.
Be sure to check with the tx manufacturer before trying.
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Old 10-04-2019, 02:12 PM   #95
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It is a simple matter of physics and hull form. Most so called trawlers you see on here are Simi-displacement and not a true round bottom full displacement hulls.

It takes X amount of HP to drive a hull to displacement speeds plus running gear drag. If the rudders are designed with very low drag and the shafts have low drag. Then if it requires for instance 65HP to drive the hull at FDS then you need 65HP on one engine or 1/2 65HP on twins plus the additional RG drag. If the diesels a properly matched to the application and running @ 80% load ( which is considered correct for most manufactures ) then to BTUs of HP required would be the same with singles or twins. Fuel burn equals BTUs energy which equals HP which equals thrust.

In most applications these formulas will hold true every time.
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Old 10-04-2019, 03:05 PM   #96
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I've always preferred the smaller (135 hp) twin naturally aspirated bullet proof diesel engines and that's what we got in our DeFever 49 CPMY. We took three years to cruise the great loop and only lost an engine twice. Once, oops, duh!, and the other was someone else's bad idea for a hose fix that was hidden until it wasn't. Both times it took less than 20 minutes to get the engine back online.

Where are you going to go cruising?

If you're an ICW traveler, with runs to the Bahamas, now and then, a single is fine. Get gold level towboat insurance. If you're crossing the ocean and it's not a Nordhaven you've got, then go for easy to access and maintain twins. Or, a newer but not new boat with known engine reliability.

I think differently today. Now, it's how easy is it to get around the engines to maintain them. The more difficult, the less maintenance will be done. The 44 and 49 DeFevers have walk-in, stoop over engine rooms (5'8") with easy access to everything. Since we had 1100 gallon fuel capacity and burned relatively nothing, we added a Gulf Coast Fuel Polishing system.

Maintained diesels are very reliable. Our current 28 foot boat is a single spit shined continuously inspected and maintained Yanmar 315 diesel with bow thruster and our next boat will be a single with bow and stern thrusters. Most likely with a Cummins 370 or 380.
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Old 10-04-2019, 03:34 PM   #97
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With a proper engine room design you can still have a twin engine configuration with ample room around the engines. The problem is that the people who design the engine room and the ones that have to perform maintenance are not the same and have very different opinions of how much space is needed.
Attached picture is the engine room on my trawler, designed by a marine engineer and not a naval architect ��.
Twin Vetus (marinized Hyundai) 65 hp each which give the ship (40’ / 15 tons) a speed of 11 knots.
Going from a single engine to a twin engine ship, I absolutely enjoy the better maneuverability, especially when you’re entering a small marina, which we happen to have a lot of in The Netherlands.
Also, being a marine engineer myself, I like the redundancy it provides. During my 40 years at sea I have seen all sorts of engines spontaneously fail, from 35 hp to 16,000 hp, most of them were being professionally maintained.
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Old 10-04-2019, 03:42 PM   #98
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IMHO, Get a single, bow and stern thrusters and for the ultimate, an articulated rudder. Would never get twins.
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Old 10-04-2019, 04:07 PM   #99
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That is one nice engine room. Plenty of space to move around. Congratulations.

No doubt twins are nice in tight spaces. The people who bought our twin screw DeFever added both a bow and stern thruster. And, I have to admit, that made maneuvering seem like you had a joy stick.
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Old 10-04-2019, 05:08 PM   #100
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What is typically talked about is one or two engines of the same relative size (double the cost, etc.). This is not true if you are willing/accustomed to travel at trawler speeds.

I went from a single 400hp boat to one with two 54hp engines. Instead of 8+ gallons of oil in the single engine, I now use 1.25 gallons --- times two. Went from $95 impellers to $20 impellers --- times two. Costs for ALL components and most services are much less, even with two engines.

Certainly affords plenty of engine room space with the small engines (attached pic).

Speaking of maneuvering, having the two engines roughly 13ft apart has HUGE advantages. Here is a video of us leaving a dock - moving the boat completely sideways using only the engines (rudder right, starboard engine fwd, port engine reverse). Bow thruster was only used at the very end of the video to avoid a fishing boat very close by.

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20180520_085404_(Medium)[1].jpg   20180520_085507_(Medium)[1].jpg  
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