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Old 09-22-2013, 10:45 PM   #281
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Thanks for the kind words and thoughts. Spending time on boats in beautiful tropical places, visiting beautiful island, where beautiful people are happy you visited is such a burden. ( Just kidding thanks)
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Old 09-23-2013, 03:13 AM   #282
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Thanks for the link. Really interesting, and not just for the boat. I don`t think people realise how poor much of Philippines is, how hard it is to get work, and to just get by. You need to know someone to get a job. It`s why so many Filipinos work overseas, on ships, as maids, nurses, carers, to support family back home. The outlying islands must be worse. A Philippines trained Doctor earns more working overseas as a nurse.
Boatgm is doing something good, really good. Slowly we see more manufactured goods coming out of Philippines, it has a huge underused potential labour force which I hope will be its eventual salvation.
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Old 09-28-2013, 02:10 PM   #283
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another WEIGHT observation

Quote:
Originally Posted by brian eiland View Post
Somewhat similar to the conclusions I was reaching,...that weight is a very important factor in ANY vessel that wants to plan off, or semi-plan. In some cases even more important than little subtities in hull shape.

It makes me wonder about the claims for much better performance by the Gerr hull shape, the SRD hull shape, the box-keel shapes etc. Are these more exagerated hull forms really that much more speed capable??

Passagemaker Magazine - May/June 2013

SRD is a better hull shape, fast, fuel efficient, stable



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Weight and length (waterline) are by far the most important factors in any hulls performance. Much smaller issues are the sectional shape, entry and exit shapes, CP and volume distribution, propulsion effectiveness, appendage drag, etc......

In general claimed superior performance is not real, or may only apply in very limited circumstances. Boatbuilders have been claiming technical advances in search of sales for ever.

I've already stated that the numbers in that Passagemaker article don't make any sense. Perhaps they did back in the time of wishful thinking before Summer Kyle was built. The original published numbers had her displacement at 16000 pounds and top speed 16 knots with 170 HP. In reality she comes in at 22,000 pounds and manages 11+ knots with 220 HP. But it will take more like 90 HP to achieve 11 knots, and not the 60HP that 3 gal/hr indicates. If she will get to 11 knots with 90HP and only tops out at 11.5 (with 220HP), I would suggest this hull would never reach 16 knots even with 500 HP.....Unhappy at speed.

Walter Schulz (SRD) is very cagy about giving out any hard and accurate numbers. He claims the SRD is "the most efficient powerboat on the market at speeds over 10 knots." but of course no numbers are available for comparison with other boats. I did some comparison years ago from numbers published in a magazine review of the SRD38. It was obvious there was no advantage to the form and I could see a standard round-bottom Lobster hull (semi-displacement) of the same length and weight would be as or more efficient.
DennisRB on another forum:
Help With Economical Semi-Planing Designs - Page 19 - Boat Design Forums

My tender is an achilles 10.5 foot with wood floor and inflatable keel with 8hp Nissan 2 stroke + foil. With just me on board 210lbs, I can accelerate from a standstill and transition smoothly onto the plane with no noticeable hump and no giant wake, with minimum throttle. I have not measured the speeds, but I can "plane" at very low speeds.

As soon as I add an extra person (much lighter than me) the behaviour changes drastically. I can no longer smoothly transition to a plane. The bow lifts and the stern digs in creating a huge wave train. Moving weight to the front assists to get it over the hump, but the wave train is still huge no matter what. Once up and planning the weight must come back to prevent the nose pushing down, and the speed can be reduced to maintain a full plane, but the speed has to be kept a lot higher than just with me aboard. The fuel burn at "trolling speed" is subsequently massively higher with the extra person.

I just thought this is a good real world example that many of us can experiment with, or have already probably had experience with, to illustrate the pronounced effect that bottom loading has on the transition to planing and power required to stay planing. It shows the concept of "semi displacement" is highly related to weight and not just SLratio. At a given SLratio between planing and displacement, the same boat can either be planing or plowing (semi displacement) with the only difference being weight.

As a side note, I can plane 3 people with my 8hp on this dingy if everything is right, which has been disputed a number of times when I have mentioned it in the past. The hull shape effectively has "hook" as the hypalon floor conforms to the flat wood floor behind the inflatable keel, it sort of acts like trim tabs trimmed down. That explains why top speed (which is pretty impressive) is achieved with all the weight as far back as possible. Actually when you think of it, the hull is a little like a seabright but with a flat instead of a tunnel, when you consider the way the hypalon floor conforms to the flat floor at the back with the inflatable keel bulging through at the front.
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Old 04-05-2014, 09:22 PM   #284
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This is a very confusing topic. So what is a light boat with a displacement type hull with hydro foils? So when its up on foils its a foiler and down in the water full displacement boat? So a semi-displacement boat at speeds under hull speed is functioning like a full displacement hull and when you fire up the twin 600Hp motors like a planning hull. Then there is the deep vee hull also in slow-mo a functioning full displacement boat and fire up the heavy metal and its 40+k. Then there is the lobster boat hull types, where most used to travel at sedate rates. Now the lobster boat races and the 500-800Hp motors have changed all that with 40+ knot speeds. Very confusing to talk about these issues.
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Old 04-05-2014, 09:58 PM   #285
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Very confusing to talk about these issues.

Ask about full displacement verse semi-planing anchors if you want to see confusing.
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Old 04-05-2014, 10:06 PM   #286
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Quote:
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This is a very confusing topic. So what is a light boat with a displacement type hull with hydro foils? So when its up on foils its a foiler and down in the water full displacement boat? ...
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Old 04-06-2014, 03:24 PM   #287
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Quote:
Originally Posted by eyschulman View Post
This is a very confusing topic. So what is a light boat with a displacement type hull with hydro foils? So when its up on foils its a foiler and down in the water full displacement boat? So a semi-displacement boat at speeds under hull speed is functioning like a full displacement hull and when you fire up the twin 600Hp motors like a planning hull. Then there is the deep vee hull also in slow-mo a functioning full displacement boat and fire up the heavy metal and its 40+k. Then there is the lobster boat hull types, where most used to travel at sedate rates. Now the lobster boat races and the 500-800Hp motors have changed all that with 40+ knot speeds. Very confusing to talk about these issues.
Well.... every boat is a Full Displacement hull when tied to the dock, and it's a waterfront condominium when aground or in the boatyard. But what is her intended use and how is the boat optimized toward that use? A hydrofoil is optimized for use at high speed riding on foils, thus it's called a Hydrofoil, and not a displacement boat. Lobster boat hulls are optimized for semi-displacement speeds, no matter what speed they are driven to they are still semi-displacement hull forms.
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Old 04-06-2014, 03:41 PM   #288
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Old 04-06-2014, 04:01 PM   #289
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Modified vee, planing type here. Runs ok at hull speed as I am too cheap to buy all that fuel. But also runs nice at 18-23kts. 11,000 miles since launch, 90% at 7.7kts and 3.9nmpg.
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Old 04-06-2014, 04:18 PM   #290
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FD.
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Old 04-06-2014, 05:06 PM   #291
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semi displacement
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Old 04-06-2014, 06:04 PM   #292
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Planing - And, I Like It. Cause... near her hull speed or just below (2.75 to 3 nm per gal doing 5.5 to 6.5 knots - 7.58 knots is calced hull speed) she uses little power and sips fuel similar to a displacement. On plane she uses fuel (1 nm per gal at 16/17 knots) - however, if desired, we can quickly get where needed. With hard chine she is comfortable in seas as well as at anchor when wakes may come to pass.
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Old 04-06-2014, 07:36 PM   #293
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Art, Re the second photo, what type of Mozzie spray do you use?
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Old 04-06-2014, 08:07 PM   #294
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Tad I am actually not confused as to hull types and what they can do and I definitely believe a hull and all aspects of a boat should be optimized for the intended use pattern. On my present boat which was built one off I tried to follow that mantra. I choose a semi displacement hull with enough power to bracket my range of desired speeds. I wanted to travel between 6 and 18 knots with the hull happy through the entire range with no discernible or major hump. This led me to the fast semi displacement type. With research I learned that pod drives( Gods greatest gift to the flagging new boat market) aside from their other attributes and faults were not optimized for the slower and mid range I desired. I have reviewed many sea trial reports of pod boats and the statistics back this up with fuel burns on pods significantly poorer between hull speed and the hump where I often like to travel say 10-14Knots. What I have noticed is that the confusion is not so much in the hull type, one look out of water and it is often apparent, the confusion is in the use pattern relative to the hull type.
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Old 04-06-2014, 09:11 PM   #295
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Art, Re the second photo, what type of Mozzie spray do you use?
No Mosquito or other flying critters all day... till about 1/2 way through the short duration of "dusk-period"... then you'd better be inside w/all screens well drawn. Or, be coated with repellent, otherwise they will carry ya away! By dawn, even just before, they are completely gone. But at dusk - BEWARE!

Can't recall brand name - As I recall we purchased several of the best they have at an REI Camping Store. Finger push pump containers - Works well!
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