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Old 01-21-2015, 01:44 PM   #121
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So what is it, on recreational boats is the protected keel thing just a "I have it so it is good," reason to get careless, sales and panacea gimmick or is it for real? BTW, good old Art put the keel below the props.
I think it's both. The protected prop and rudder on the typical single engine cruiser defintely offers some protection against debris and from "gentle" groundings on mud or sand bottoms.

But I'm aware of more instances of people with single engine boats (including sailboats) fouling their prop on crab pot lines or other debris than I am of people with twins doing the same thing. So this plus what I read on this forum from time to time would indicate there may be a false sense of security at play, too.

I think for the most part people with twins are very much aware of the potential vulnerability of their running gear and so take particular care to avoid hazards in the water.

We certainly do, steering around things like eelgrass and kelp mats, picking the best path through a debris-laden tide or current line, and keeping a sharp eye out at all times for things like branches, logs, lumber bits, crab and shrimp pot floats and so on.

If the light is such that it makes these things hard to see, or if we're in an area crowded with pot floats we put two peopke at the helm to better our chances of running over something.

Our boat doesn't have an autopilot anymore and this is one advantage of hand steering in waters that can have quite a bit of debris in it in that the helmsperson is always aware of what's in front of the boat because he or she can't leave the wheel and get involved in something else.

I'm not advocating not using an autopilot by any means-- most of the people we know who have and use them seem to be every bit as vigilant as we are, although we know a couple of people who have them but don't use them because they are more comfortable hand steering when there's lots of stuff in the water.

And the bottom of the keel of a GB twin is lower than the props and rudders by a fair amount which is beneficial if the boat touches ground while docked or moored during a very minus tide.
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Old 01-21-2015, 02:08 PM   #122
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I'm confident that I am not ever completely confident I will not hit something in the water... whether it is a single or twin screw boat. However, I am absolutely confident that I have better chance of missing floating debris, or semi submerged debris, and of noticing shoals while piloting from flying bridge. I try to not need to travel at night and if that need arises, I'm confident that a clear night during full moon is best... because at least some light reveals what a dark night can hide. Depending on speed a really good spotlight is useful too!
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Old 01-21-2015, 04:26 PM   #123
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I also don't know when and if I am going to run my boat aground or hit a significant log, but if it happens it will most likely be because I was not properly vigilant and a protected prop may help but would not guarantee no damage or even less damage. I do agree with my twin bare props I am much more careful than I was with my many FD boats with protected props and I grounded much more often with those boats since I worried less and paid less attention. Bare props makes me a better helmsman and navigator by necessity.
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Old 01-21-2015, 04:42 PM   #124
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I run a bare prop. It does pucker you up in skinny water. When I built my boat, I made a decision that the drag of a keel and the prop induced vibes from it outweighed the benefit of the protection. My boat is dual purpose, lots of 7.5kts, but also capable of a 20kt cruise, and there the skin drag of a keel is significant.

If I ran exclusively at 7.5kts, I would have added a skeg keel.
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Old 01-21-2015, 05:14 PM   #125
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I run a bare prop. It does pucker you up in skinny water. When I built my boat, I made a decision that the drag of a keel and the prop induced vibes from it outweighed the benefit of the protection. My boat is dual purpose, lots of 7.5kts, but also capable of a 20kt cruise, and there the skin drag of a keel is significant.

If I ran exclusively at 7.5kts, I would have added a skeg keel.
Representing - Planning hull being 35' lwl x 12' wlb at 20 knots:

I wonder what the additional drag coefficient really is for the following keel.

- Single, 4" thick center keel
- Tapered from 0" at stem
- 24" depth off boat bottom at skeg

Bet cha some one has a formula handy... maybe Ski or Tad! Or...??
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Old 01-21-2015, 05:18 PM   #126
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Greetings,
Mr. A. Double it and add 32. That'll give you a metric conversion.
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Old 01-21-2015, 05:20 PM   #127
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Marin thanks for the Spray update. I'd go w another color too.
In your pic it looks like the windows have been modified .. made bigger like the NT.

eyeschulman,
Just my opinion but I don't think any boat w a straight run aft is anything but a planing hull unless they have a very big keel. To get out of the planing catergory IMO it would need some rocker. Don't see it. Is the designer SD? I think he's thinking about marketing. He does that well.
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Old 01-21-2015, 05:28 PM   #128
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We've run over gillnets and long lines and never fouled the prop after 16K miles on Hobo and 40K plus miles on our sail boat. The paravanes have caught stuff though.

On our 1966 27' Chris Craft Commander (single, unprotected prop) we pulled the prop at least every year because we hit/caught something. Maybe the difference was the speed, 7 knots vs 15 plus? It wasn't for the lack of paying attention since we never ran the Chris Craft at night and no auto pilot like Marin.

Pics Hobo's bottom
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Old 01-21-2015, 05:32 PM   #129
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Greetings,
Mr. A. Double it and add 32. That'll give you a metric conversion.
That equation and a "dollar three eighty" plus tax... might get cha a cup o' java at the boat shows!
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Old 01-21-2015, 08:25 PM   #130
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Marin thanks for the Spray update. I'd go w another color too.
In your pic it looks like the windows have been modified .. made bigger like the NT.
I don't know. In the black and white photo the window frames appear to be painted black or some dark color, where in the more recent photo the frames are white. This actually makes the windows in the aft cabin appear smaller.

But it's very possible things have been rebuilt some in the fifty-odd years that have ensued since Spray was launched.
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Old 01-21-2015, 08:45 PM   #131
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How much ??? is a dollar three eighty ? It does however make about as much since as folks on a "trawler" forum touting go fast boats. I presently own both ends of this spectrum but I am not a member of any go fast boat forums either. It does seam like the knowledge base is a lot deeper on trawler or "go slow" forums, go figure. My personal opinion is that everyone wants to be like the real trawler guys, kinda like "closet trawlering" except they're wanting folks to think they have a trawler instead of a speed boat. Apparently trawler is cooler. To me it is not a mindset or type or lifestyle, it is a "boat" that is easily indentified once you know it. It is NEVER fast, or any thing close, it cant be stepped up to beat weather, it has to be built to handle it. It doesnt slow for weather, its slow enough already. It typically has long legs, not just hunnerds of miles but thousands. It requires some form of stabilization to be habitable in any kind of sea state besides flat. Round bottom and all, kinda rolly. How many here actually own a FD trawler ? And not some speculation as to whether or not your hull really is FD or if your boat is a trawler, I mean the real thing. JMO
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Old 01-21-2015, 09:18 PM   #132
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Marin thanks for the Spray update. I'd go w another color too.
In your pic it looks like the windows have been modified .. made bigger like the NT.

eyeschulman,
Just my opinion but I don't think any boat w a straight run aft is anything but a planing hull unless they have a very big keel. To get out of the planing catergory IMO it would need some rocker. Don't see it. Is the designer SD? I think he's thinking about marketing. He does that well.
Just some pictures of lobster boat butts. These boats are operated for the most part in SD mode and it takes very hefty power to approach planning but still no hump to jump. Yes the butt angles are flat. If my boat was done as a single it would have the same keel as pictured and a very similar hull shape. I do think the functional differences are murky and don't match the old buttock angle definitions.
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Old 01-21-2015, 09:49 PM   #133
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How much ??? is a dollar three eighty ?
Don't forget the tax! "Dollar three eighty plus tax" is an old NY slang about some low value item in a store that has no $# attached. So, when asked how much does it cost... to break the ice, you could make the funny remark... Oh, it's about a dollar three eighty plus tax. A double take is nearly always the response with a tilt of the head and the question... What did you say??? Not too unlike your question, followed by three ???
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Old 01-21-2015, 09:51 PM   #134
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Just some pictures of lobster boat butts. These boats are operated for the most part in SD mode and it takes very hefty power to approach planning but still no hump to jump. Yes the butt angles are flat. If my boat was done as a single it would have the same keel as pictured and a very similar hull shape. I do think the functional differences are murky and don't match the old buttock angle definitions.
But everything evolves. It's like spin offs of tv shows. From Lobster boats, along came Downeast boats and they definitely aren't SD.
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Old 01-21-2015, 10:00 PM   #135
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Good answer, both ways.
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Old 01-21-2015, 10:17 PM   #136
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Don't forget the tax! "Dollar three eighty plus tax" is an old NY slang about some low value item in a store that has no $# attached. So, when asked how much does it cost... to break the ice, you could make the funny remark... Oh, it's about a dollar three eighty plus tax. A double take is nearly always the response with a tilt of the head and the question... What did you say??? Not too unlike your question, followed by three ???
Wifey B: Sure glad you clarified as I'm not old or NY so sure had no idea what it meant.

It's like the song "25 or 6 to 4."
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Old 01-21-2015, 10:40 PM   #137
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Wifey B: Sure glad you clarified as I'm not old or NY so sure had no idea what it meant.

It's like the song "25 or 6 to 4".
Wifey

Didn't say I am old... just that the saying is old NY! Gran Pa Arthur taught me that one while I was in grade school. I'm 38; been holding there for couple decades! - LOL

That is a good ol' party song! I recall it well and just listened again... first time in years!

4 am is the hour where parties get long of tooth... been there, done that... when young!

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Old 01-22-2015, 01:24 AM   #138
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The torpedo boat is planning the blue boat is traveling in SD mode faster than hull speed but not lifting onto a stern planning surface as seen with the TB. The old buttock angle definition separating planning from SD is of little value if a boat with a flatter angle is in all other ways set up to run with most of its hull in the water in a SD mode. This is where the definitions get murky and lose a lot of their value. If the boat never gets on a full plane why call it planning not that it maters what you call it it's how it runs. The blue boat can keep that same angle of attack up to 18+k with almost full length of WL still in the water. Or do we call it full displacement planning? Or total hull distribution planning?
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Old 01-22-2015, 01:45 AM   #139
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Reminds me of the Sheriff's boat zooming past me last Saturday.
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Old 01-22-2015, 08:25 AM   #140
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The torpedo boat is planning the blue boat is traveling in SD mode faster than hull speed but not lifting onto a stern planning surface as seen with the TB. The old buttock angle definition separating planning from SD is of little value if a boat with a flatter angle is in all other ways set up to run with most of its hull in the water in a SD mode. This is where the definitions get murky and lose a lot of their value. If the boat never gets on a full plane why call it planning not that it maters what you call it it's how it runs. The blue boat can keep that same angle of attack up to 18+k with almost full length of WL still in the water. Or do we call it full displacement planning? Or total hull distribution planning?
I call it "semi-planing-pretty"!

planing hull
noun, Nautical
1. a hull that tends to rise from the water when under way so that no significant amount of water is displaced beyond a certain speed.

displacement hull
noun, Nautical
1. a hull that displaces a significant volume of water when under way.

semi-displacement hull
noun, nautical
1. a hull design incorporating displacement and planing water attitudes.
2. exceeds displacement hull speed limitation.
3. below speed potential of planing hull.
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