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Old 11-09-2013, 07:04 PM   #1
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Weight Distribution

This post was in response to something Art said but so far off topic I'm posting it here.

Weight placement and ballast is not a hard line cast in stone thing. However you are very right otherwise but just because a boat is not home built or home designed or both dosn't mean it was marketed as ideal.

When I worked at Uniflite for a time I was in charge of re-arranging the installed location of heavy equipment .... Batts, holding tanks, gen sets, water heaters ect ect. The necessity for me to do that arises from the fact that most all the boats were different so we had to get a pool of information that could be referenced to a known configuration that resulted in a boat that would when launched float without a list. Obviously w a stock boat it wouldn't be necessary.

But frequently the same hull is used for boats w extreme differences in weight distribution. Have you ever seen a boat that is offered as an twin engined IO and also a single engined OB? Not uncommon at all. And a straight IB on the same hull as V drives w the engines in the stern.

I, to some extent fear having a bow heavy boat in following seas. And I'm a bit over ballasted in the stern than a stock Willard. And speaking of Willard's some have their engines further fwd than others.

So it's common for fairly significant variations to exist on stock manufactured boats so it would seem that fairly small changes in weight distribution should not be a problem. However if one has a boat w twin IOs adding weight like an extra battery, water tank or other stuff that represents some weight mounting it fwd would seem best. Making a bad situation worse is a real possibility. The perfect boat (in my opinion) would have most heavy things quite close to the center of then boat or slightly aft. Or if one had a port list and then installed a gen set on the port side ....
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Old 11-09-2013, 09:06 PM   #2
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I've been thinking about that. I just yanked my 400 lb. genset from below the galley and will be installing it in a new hatch in the veranda....basically moving 400 lbs. from 10 ft. forward of the main engine to 4 ft. behind the main engine. The boat was beautifully balanced as was. For partial compensation, my plan is to move both 8D house batteries into the old genset space below the galley which are now a foot or so behind the main engine. The addition of more chain and two heavier anchors on the pulpit might do the rest. The weight is not that big of a deal, but the distribution may be.
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Old 11-09-2013, 09:23 PM   #3
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Weight distribution isn't rocket science... nor is it childs play....

All the weight does not go low and in the center unless you really like a boat with a snap roll and one that hobby horses.

You need some weight at the extremities to make the waves overcome some mass...so spreading the weight around is actually a good thing most of the time...

....but significant changes require some sort of calculations even if it's just a backyard yardstick (if you understand the principles) and once they become really significant...some basic stability test should be done to put your mind at ease let alone the insurance companies.
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Old 11-10-2013, 12:11 AM   #4
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Quote:
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This post was in response to something Art said but so far off topic I'm posting it here.

....
Here is quoted the the full extent of "something" that Eric was referring to on what I [Art] said:

"Irrespective of its need for care... On another slant regarding teak (or anything of weight)...

Every hull design and size boat has an optimum weight as well as optimum distribution areas aboard said boat of the individual items that comprise its total weight.

Therefore, I remark:

To add extra weight that any boat was not originally designed for (engineered to correctly accommodate) that weight may become problematic in the grand scheme of the originally engineered plans that rule a boat’s “living” composition.

Not all, but most, boats have considerable marine engineering aback their design and weight ratios/placements. I’ve found that interfering too much with the educated marine engineer’s initial weight-ratio-placement considerations can develop problems under certain sea conditions.

Weight placements/additions aboard any boat should receive close scrutiny as to developed effects the “new” extra-weight may provide.

Smaller the boat... more easy it is to override the boat’s originally engineered hull-plans with even minor additions/placements of weight.

Jus sayen!

Happy Boating Daze! - Art"
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Old 11-10-2013, 06:39 AM   #5
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Weight placements/additions aboard any boat should receive close scrutiny as to developed effects the “new” extra-weight may provide.

Sure , but a -1% change is hardly a big deal in most boats.
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Old 11-10-2013, 07:36 AM   #6
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Having a small and fairly lightweight boat, weight placement can be affect our boat a lot. A friend with a Nimble once asked me why I thought his boat had a definite lean to port? I told him the fact that his hot water heater,his water tank, and fridge all being on the port side might have something to do with it! Most Nimbles did not come with HW heaters installed or built in AC so planning the placement is critical.
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Old 11-10-2013, 09:22 AM   #7
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So far the discussion has been weight distribution in terms of fore and aft, port and starboard. Many of our trawlers have upper decks (boat decks) and the specifications for these boats have limits on how much weight can be put on these decks without compromising stability. I was told many years ago that for my Krogen 42 this was 750 pounds (340 kg) and included the weights of any helm chair, the dinghy, motor, equipment and the crew on the deck. I have a 3.2m dinghy and a 9.9 hp motor (2 stroke), but with the helm chair a couple of dock boxes, winches, windlasses and some equipment I am close enough to the 750 lbs that when I am on the deck we are over the limit. In my case this is not a problem because we are never on the upper deck in heavy weather.

It is possible that many others are violating their weight limits on the upper deck without even knowing it. Especially with a larger dinghy and motor.

Marty
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Old 11-10-2013, 10:12 AM   #8
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Marty wrote;

"It is possible that many others are violating their weight limits on the upper deck without even knowing it"

Sure. Many or more don't even think about that. And I'm sure most manufacturers assume that over time a boat will get heavier as people tend to add things to their boat much more than take things off and to minimize the building cost most boats are probably minimal in weight when new.

FF I think we're all talk'in considerably more than 1%.

Hustler that's what I did at Uniflite. Also the best place for equipment was also considered in the shuffle. Didn't put batts in the laz or or gen set by the berth. But often compromises were made.

Nimble1 I've found the big problem w small and light boats is that everyone wants to sit on the same side of the boat and dosn't even notice the heavy list. Whale ..........
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Old 11-10-2013, 10:19 AM   #9
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Hustler that's what I did at Uniflite.
Eric: What years were you at Uniflite and why did you leave? Did you retire from there?
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Old 11-10-2013, 10:41 AM   #10
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Quote:
Originally Posted by Bay Pelican View Post
So far the discussion has been weight distribution in terms of fore and aft, port and starboard. Many of our trawlers have upper decks (boat decks) and the specifications for these boats have limits on how much weight can be put on these decks without compromising stability. I was told many years ago that for my Krogen 42 this was 750 pounds (340 kg) and included the weights of any helm chair, the dinghy, motor, equipment and the crew on the deck. I have a 3.2m dinghy and a 9.9 hp motor (2 stroke), but with the helm chair a couple of dock boxes, winches, windlasses and some equipment I am close enough to the 750 lbs that when I am on the deck we are over the limit. In my case this is not a problem because we are never on the upper deck in heavy weather.

It is possible that many others are violating their weight limits on the upper deck without even knowing it. Especially with a larger dinghy and motor.

Marty

The upper deck weight is another thing I have been concerned about, especially in weight overhead of the pilothouse. When re-skinning my pilothouse roof, I saved about 45 pounds over what came off, but I also raised the radar and Sat. TV onto a new mast. Total weight of mast and devices are 90 lbs., most of which is above the roof line. Now the idea is to mount solar panels on the cleaned roof along with bracketry... another 110 lbs.. Then the Stidd helm chair, 80 lbs.. The typical big dock box behind the pilothouse as it was before (120 lbs.) will likely go in two smaller units on the bow. CG of my boat, according to the spec' sheet is 19" above waterline with half tankage. When you're talking about putting a lever of weight 15 ft. north of that, it may not mean much when the boat is level, but at 30 degrees?!
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Old 11-10-2013, 10:45 AM   #11
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Haha Walt,
Only worked there for awhile. Two years I think. The assistant chief engineer didn't like the fact that I didn't think the Uniflite was the best boat in the world. I said Florida built boats had more class ect. Also I was not a grade A draftsman and too slow. A cleansing of the drafting room was made. It was in the early 70s.

That was a personal question but ??? I'm open.
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Old 11-10-2013, 10:52 AM   #12
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It is possible that many others are violating their weight limits on the upper deck without even knowing it. Especially with a larger dinghy and motor. Marty

Or how about those that:
  • Enclosed the FB with a hardtop and Lexan
  • Put a chest freezer or two on the Sundeck or on top for the fish
  • Get rid of the 30 year old Lehman 6 and put in a new 60 hp Yanmar
  • Put 20 people on the FB of a Silverton at a fireworks show
Yup, there are lots of ways to raise the CG.
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Old 11-10-2013, 10:53 AM   #13
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Weight limits topside are often a structural related limit rather than stability....always best to check to be sure..

Weight and stability isn't an all or nothing issue...it's gradual. Keep adding weight and the stability can "get worse" but even then there are times you want a slower roll as has been posted many times.

On the USCG Icebreakers...we used to have to go out and use circus mallets to break ice off the upper structures when it got too much...on the Polar Class 399 footers I believe it was when the ice was estimated at 20 tons...that's when the mallets came out.

After that Silverton tragedy last 4th of July in Long Island Sound...there have been government discussions on more strict guidelines to the average boat owner in the owners manuals and stickers/placards.
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Old 11-10-2013, 11:04 AM   #14
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That was a personal question but ??? I'm open.
It wasn't meant to be a personal question...I was trying to get info on exactly when Uniflite developed the fire retardant fiberglass and thought you might have been aboard when that went down.
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Old 11-10-2013, 01:04 PM   #15
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It wasn't meant to be a personal question...I was trying to get info on exactly when Uniflite developed the fire retardant fiberglass and thought you might have been aboard when that went down.
Uniflite was ordered by Uncle Sam to use the fire retardant resin due to some 700 +/- 31' patrol boats ordered for Viet Nam Delta Patrols. the new resin mix became used in govt boats by early 74 and it gradually worked its way into all Uni boats by mid 75. That is what i was told by a Uniflite founder I spoke with years ago while I owned a blister free 1973 31' convert-sedan FB twin screw Uni. Real nice boat!!
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Old 11-10-2013, 02:12 PM   #16
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In my opinion, planing and semi displacement vessels should be trimmed slightly up at the bows. The bow can be lowered at speed by tabs or wedges but can not be raised when needed except by ballast tanks. In general, weights sould be kept out of the ends but spread laterally.

Uniflites were great boat for their times and prized for restoration in these parts unlike so many others of their era.
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Old 11-10-2013, 02:27 PM   #17
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In my opinion, planing and semi displacement vessels should be trimmed slightly up at the bows. The bow can be lowered at speed by tabs or wedges but can not be raised when needed except by ballast tanks. In general, weights sould be kept out of the ends but spread laterally.
That was Charlie Jannace's advice to me when I was considering adding more anchor chain for weekend dive trips to the middle grounds on one of his designs.

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Old 11-10-2013, 03:30 PM   #18
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Walt,
I didn't have anything to do w the patrol boats. Worked on the 26' whaleboats. Installed engine mounts, rudder ports and shaft logs. That was before I went to engineering.
I don't know anything about the resin and at the time I was there there was no such word as "blister".
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Old 11-11-2013, 05:46 AM   #19
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>I was trying to get info on exactly when Uniflite developed the fire retardant fiberglass and thought you might have been aboard when that went down.<

FR resin was used in industry for mant years before the US wised up.

Most duct work in large factories is FR plus additives to bringing the burn rate down.

Fuel tanks also are FR.

Normal cheapo resin burn rate about 500

FR resin (2c a pound more) burn rate about 100 like oak.

With chemical additions as low as 3 can be done but at a cost of about 3% reduction in overall strength.
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Old 11-11-2013, 10:55 AM   #20
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The PO installed a third fuel tank which increased Badger's fuel when full from 100 gallons to 140 gallons...sits a bit arse heavy when full, especially if the 50 gallon water tank is full too. All four sit in the lazerette.

We like the extra fuel, especially on BC's north coast where fuelling stops are so far apart, when the smaller isolated ones regularly run out, and when there's so much to see in between them up loooong channels and inlets.

We usually fill up plastic jugs with creek water as we go along and don't fill the onboard water tank to the brim since we stop every day to go ashore for photographing and walking the dogs.

As you can see, water stops are not a chore;
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