Outdoor build of GA Kodiak, Orange, CA

[json]

Good info. I have been thinking of ways to move weight aft, specifically because I am looking at getting a bow rail done and I am not sure how much weight that's going to add up front in addition to what's already there. I am wishing I would have put in 2 fuel tanks instead of the 10 foot long single, because I think that exacerbates the issue to a degree. The 2 things I can come up with are the house batteries (120lbs) and the inverter (65 lbs), which are both inline with the helm. I think I can find a way to move the house batteries aft (albeit with some pretty major surgery), pretty close to the back of the cockpit, the inverter is going to be a little more challenging because it needs ventilation to keep from overheating. Beyond that there isn't a ton of stuff up there besides the giant winch on the front of the boat. I am going to have to look a little closer at how it trims loaded and ready for a trip (with 3 or 4 people in the cockpit), I think the bait tank being full helps but doesn't quite get there, hopefully some ice in the fish box also helps. I am not really seeing any real ill effects of the bow heavy trim, at least that I have noticed, other than the bow being low looks kind of silly. In any event, work in progress...

[Brian.Dixon]

Doing the best that you can is always a good idea, but I wouldn't fret too much.  If it's trimming up or down a little, you won't see it and it'll perform well regardless.

[Todd j]

Mine is a tad bow down too.  Maybe 2” in 20’.  No one has even noticed.  Little more with sleepers in the cuddy.  The stern is steady having some lbs. 

[Brian.Dixon]

Mine is a tad bow down too.  Maybe 2” in 20’.  No one has even noticed.  Little more with sleepers in the cuddy.  The stern is steady having some lbs.

Every time I see a little bow-down trim, I wanna pull my hair out!  As mentioned before, you measure the waterline from where the bow cuts water aft to where the waterline ends on the transom.  That's your at-rest waterline length, and it's a design parameter (the 'design waterline' or DWL).  For a PLANING hull, the window where the CG should land is 60-65% of that waterline aft of where the bow cuts water.  When the CG is in this window on the GA, the boat trims up at the bow over 2".   In any case, the CG location highlights that 2/3rds of the boat is f'w'd of the CG and that boats loaded for bear ... er, camping ... and are outfitted better than most single-wides are very likely to be heavy f'w'd ... hence the downward trim.  Note, however, that the Great Alaskan was designed very conservatively and it performs equally well when the bow trim is plus or minus about 3" at the bow versus the stern.  I may produce a 'camper special' version of the boat(s) at some point and include some minor mods ... slightly wider amidships or slightly forward, perhaps slightly narrower at the stern, evaluate the hydrostatics with a full suite of items in the house and cuddy to determine trim, allow the stringers to slope upward towards the bow by the trim angle (the 'new level definition' for the boat).  We're trying to work a bit of magic here ... load up a planing hull as though it were one of those fancy beauts designed by Sam Devlin, but keep the CG in the right window and achieve the most optimal trim.  People are adding a lot more weight forward than I'd imagined for the original design ... BTW, to see perfection on the water in terms of CG and trim angle, go see Dave Collette-Paule (sp?)'s boat in Homer, AK.  He's got a super sweet 26-footer that I fell in love with after just one ride.  Nice guy too.  Both him and his wife (and wife's mother) - make sure you  insist on their homemade pizza if you visit!  In any case, the saga never ends and I'll continue to tune the design over time.  In the mean time, keep that weight aft!  As I've suggested many times (but nobody has done it), consider NO forward tank if you're going to build a camping boat and use the whole under-deck area in the cockpit for fuel, and just behind the aft house bulkhead (or even right through the bulkhead), add saddle tanks under the sheer deck on either side to gain back the fuel capacity lost by eliminating the forward fuel tank.  That alone will trim out the boat nicely.  Put fish wells or live tanks on TOP of the cockpit deck.  I'm rambling ... I'd say "to make a long story short" but ... too late!

[Todd j]

I hear your frustration.  I’m judging my bow down at rest by the line of the bottom paint on my boat.  Your 100% right about adding much stuff to the inside.  Dan B raised the bar for comfort and handy stuff.  I would have saved 1000$$$$$$ if he built after me.  Having said that, I have not 1 single complaint.  You can only do what you can do and we’re going to do what we do.  There’s only so much room for “stuff”. Each decision dictates the answer to the next question.  Who wants a cookie cutter boat?  That’s why the GA is so awesome.  It seeMs to be pretty forgiving.  The guy who designed it must have known what he was doing!

[Brian.Dixon]

In my experience, the trim is more aesthetics than anything.  The boat works the same, same performance, same everything from what I can see.  Almost all 'camper' boats are displacement vessels (re my reference to Sam Devlin's beautiful boats, people converting trawlers into live-aboards etc).  It's a battle when you're trying to do it in a high speed planing hull ... it takes real effort to keep the CG in the right 60-65% waterline location.  But as mentioned before, I designed the boat very conservatively, expecting people to do a wide variety of things with them, and to load them in a wide variety of ways ... and boy have they!  But pay close attention ... no bad behavior, bad habits, or inability to plane etc etc has ever been identified with these boats and they've been on the water since about 2005 ... 18 years ago now.  They're proven.  I'm not aware of any other DIY boat that performs as well or provides so much for the money. 

[Dan Boccia]

I consider my boat actually quite simple, plus the cabin is largely built with foam-core instead of plywood so my cabin is very light. One single 85 AH AGM house battery, no shore power or AC system with inverter, no propane system, no built-in cooktop or range, no built-in water tank/plumbing, no head. My boat always performs measurably better (by way of mileage and speed over ground improving) when I trim the engine and use the trim tabs to get the bow down slightly from it's natural position, so I'm clearly not bow heavy. When I sleep I'm actually a bit too much bow-up and still wish I had built my bunks with a bit of a taper rising aft.

One of the main changes over the past couple years is that people are (rightfully so) installing lithium house batteries, which can go inside the cabin since they do not have to be ventilated. The problem is that they have ended up under the helm seat, which moves the considerable weight of a house battery system from somewhere like just aft of the aft cabin bulkhead (where Brian designed it I think) to far forward of Brian's CG. I encourage people to put the lithium battery system in a locker just forward of the aft cabin bulkhead, with inverter just aft of this bulkhead (which means very short large wire runs), putting all this weight right at the CG, but so far have been outvoted because this is prime real estate for hanging and/or wet gear lockers/heads that people want.

[Todd j]

I consider my boat actually quite simple, plus the cabin is largely built with foam-core instead of plywood so my cabin is very light. One single 85 AH AGM house battery, no shore power or AC system with inverter, no propane system, no built-in cooktop or range, no built-in water tank/plumbing, no head. My boat always performs measurably better (by way of mileage and speed over ground improving) when I trim the engine and use the trim tabs to get the bow down slightly from it's natural position, so I'm clearly not bow heavy. When I sleep I'm actually a bit too much bow-up and still wish I had built my bunks with a bit of a taper rising aft.

One of the main changes over the past couple years is that people are (rightfully so) installing lithium house batteries, which can go inside the cabin since they do not have to be ventilated. The problem is that they have ended up under the helm seat, which moves the considerable weight of a house battery system from somewhere like just aft of the aft cabin bulkhead (where Brian designed it I think) to far forward of Brian's CG. I encourage people to put the lithium battery system in a locker just forward of the aft cabin bulkhead, with inverter just aft of this bulkhead (which means very short large wire runs), putting all this weight right at the CG, but so far have been outvoted because this is prime real estate for hanging and/or wet gear lockers/heads that people want.

I was referring to the fridge, winch, Wallas, and solar mainly.  I didn’t even know I needed that stuff until I saw it on your boat.  I’m very glad you got there before me!  I have those goodies too and wouldn’t be without any of them now.

[Brian.Dixon]

Great post, Dan.  I designed the Kodiak, based on the original Great Alaskan, to be longer and have more stern capacity ... a work boat, with more crew and gear in the stern that you'd typically find in a GA built for a couple to cruise in.  It seems most are far more interested in the cruiser concept rather than the work boat, which means I should tweak the design to support that type of usage.  Building house and cuddy sides and roof with foam-core, moving the aft cuddy bulkhead (and whole pilot house) aft by a foot, chine flats widest f'w'd and tapering narrower aft (perhaps to the original GA chine flat width and then use the same transom), and add information to the manuals that show green zones for the heaviest items, yellow and red zones further from the CG.  Perhaps by default, raise the cockpit deck a goodly amount and specify a large aft belly tank that uses this full volume ... suggest saddle tanks for more range and capacity instead of a forward belly tank.  Lots of ideas.  I'll start by adding less-ambiguous guidelines to the manuals...

[Dan Boccia]

Brian, I love that you share your thoughts on the boat's design and how you can or have tuned things to get a certain weight balance. This is super helpful to all of us building these things. Thanks!

[Brian.Dixon]

Thanks for the kind words, Dan.  Your contributions to the cause have been fantastic and MUCH appreciated too.  We'll have to meet up at Moose's Tooth or somewhere next time my wife and I come up ...

[json]

After speaking with Brian some I have decided to try to get my trim in better balance. I built with a few misunderstandings that were amplified as my build went on, which are probably only going to get worse as I continue to outfit the boat moving forward. The goal of my build was to create first and foremost a fishing boat, with a lot of space in the cockpit. I pushed my house forward and shrank the cuddy to some degree in order to maximize the space aft, which was the first item that started the issue. Then I positioned my fuel tank in reference to the moved forward aft ph bulkhead which was forward of the cg. I used a single 10' center fuel cell that I positioned 6" further forward still in order to offset the bait tank I was going to use, which would be 80-120 gallons, so 750-1000 lbs, but it turned out that my bait tank actually landed just about on the CG, so the offset only served to further amplify the issue. With the length of the fuel cell, the bow heavy trim causes the fuel to pool forward, which amplifies it even further still. Finally, I put an EZ rebel 5 on the bow, and 22 lb anchor, and combined with a rather light weight yamaha outboard, the end result is a pretty forward heavy trim. After conferring with Brian, we came up with a plan of items that I can consider to recalibrate the approximate trim of my boat. I used the CG that he gave me and did some computation about the net effect that different items will have on the trim of the boat.

CG on my boat will be approximated at 9.5 ft forward of the transom

Bow influencers -

Fuel tank (1/2 full 585 lbs of fuel, approximating the cg of where the fuel sits by moving it forward a bit to compensate for the pooling effect): +2.5 ft <- CG, 1462.5 ft lbs of torque
Anchor system: 172 lbs, +17.5 ft <- CG, 3010 ft lbs torque
Inverter/charger: 55 lbs, +8.5 ft <- CG, 467 ft lbs torque
House batteries: 84 lbs, +7.5 ft <- CG, 630 ft lbs torque

Stern influencers -

Starter battery: 63 lbs, -7 ft -> CG, 434 ft lbs torque
Bracket: 63 lbs, -10 ft -> CG, 630 ft lbs torque
Motor: 560 lbs, -11.5 ft -> CG, 6440 ft lbs torque

Brian concluded that the fuel tank and the winch were the biggest offenders, which they turned out to be. So, I put together a list of potential things that would influence a stern down trim, and am thinking I will start to try to negate the effects of the torque applied by those big offenders.

Adding 4" to motor bracket of current outboard nets an additional 168 ft lbs of torque to stern
adding a 25 hp yamaha kicker (150 lbs) nets 1500 ft lbs of torque
moving the batteries aft to within a foot of the transom nets 1344 ft lbs of torque
moving the inverter to about the same place as the batteries nets 852 ft lbs of torque
adding a 40 gallon fuel cell where I currently have a fish box nets 1560 ft lbs of torque (noting that this would actually do far more, since this fuel almost always would be also removed from the front tank)
replace my current outboard with a pair of yamaha 150s nets 4110 ft lbs of torque

The values were a bit surprising to me, specifically how little correction I would gain putting the motor on a bigger bracket. If I install a kicker and move the batteries and the inverter aft I will offset the whole influence of the anchor system. The batteries wouldn't be difficult but the inverter has ventilation requirements that will make it a bit more challenging. Or I can just go for the gusto and put twins on it. I think my wife will probably approve of option 1 far sooner than option 2.

I think my next step is to do a little verification down at the launch, put the boat in the water, and see how much a specified amount of torque will influence the trim, like put a couple 200 lb people on the swim step and see how it trims then (which would apply 3600 ft lbs of torque aft) to see if the work will get me there or not. Either way, I am getting my winter projects lined up!

As a side note, I ended up selling my first trailer (kokopelli 7k gross) and getting a new trailer custom built for the boat by west coast trailers here in town that's 10k gross. The owner Wayne measured everything, moved the position of the axles forward a bit, and was able to fit it to my boat much better. It's wider, a bit shorter, and far more stout. My old trailer was built for a cigarette boat, never fit quite right, and had a receiver that was rated for 500 lbs which I had more than 1200 lbs on. I didn't realize how badly I was white knuckling towing until I pulled my boat home on the new rig, it tows like a dream now. The tongue is still heavier than I would like but hopefully some of these improvements will also get that more in line. I initially reached out to them with hopes that they could move my axles forward on my kokopelli, which wasn't really that feasible, then started talking about rigging it with heavier axles, and ultimately it was going to cost as much to do the work as just getting a new trailer would. End result was expensive but is considerably more safe. Every time since then that I have towed the boat I am really happy I made the choice.

[Brian.Dixon]

If the inverter really is best off in the house, for ventilation, perhaps just moving it to just inside the aft house bulkhead would at least reduce it's negative affect?

2X 200# people on the swim step ... or just me alone!  Ha!

Let us know, in inches at the bow, how the trim changes for a given weight on the stern ... that'll calibrate your efforts.

[Rbob]

quote:  As mentioned before, you measure the waterline from where the bow cuts water aft to where the waterline ends on the transom.  That's your at-rest waterline length, and it's a design parameter (the 'design waterline' or DWL).  For a PLANING hull, the window where the CG should land is 60-65% of that waterline aft of where the bow cuts water.

I may be a little slow, if Json or anyone measures that at rest waterline do you compare it to the overall length of the boat to see if the CG is 60-65% or?

Heavy bow = longer at rest waterline I understand that.

[Brian.Dixon]

quote:  As mentioned before, you measure the waterline from where the bow cuts water aft to where the waterline ends on the transom.  That's your at-rest waterline length, and it's a design parameter (the 'design waterline' or DWL).  For a PLANING hull, the window where the CG should land is 60-65% of that waterline aft of where the bow cuts water.

I may be a little slow, if Json or anyone measures that at rest waterline do you compare it to the overall length of the boat to see if the CG is 60-65% or?

Heavy bow = longer at rest waterline I understand that.

Yup, those are the magic numbers.  As far as trim goes, it's the combination of the center of buoyancy (CB) and the center of gravity (CG) that determines it.  Both move with loading and different trim angles.  And to complicate matters, every boat is different and the only way to predict exactly what the trim will be would require a very detailed center of gravity analysis ... every teensy thing that's in the boat goes into that spreadsheet.  BUT, to some degree on that, we're splitting hairs.  Knowing approximately where the CG should be and balancing weights on either side of it (fore/aft that is) is a rule of thumb kind of thing ... hence json's upcoming exercise in putting a known amount of weight on the stern and measuring the resulting change in trim.  I'm happy if the end result in trim ranges from 2" down at the bow to about 3" up at the bow - If your boat's in that range and you don't like how it looks then paint a new bootstripe or waterline on the boat and keep going.  I also like to point out that these boats are light for their size and that weight distribution has greater impact on them than on a big heavy boat, e.g. an 11,000# 26-ft Orca or similar ... which is fine and one of the main factors that results in higher mileage (efficiency) ... but just be educated on the topic.  Example) Gonna sleep in the boat? You'll be bow-down all night and it might rain ... block water routes forward and back that up with a small bilge pump under the cuddy deck/floor or forward end of the house decking, oh and don't drain anchor wells or other things into the bilge .... keep'r dry!

PS: Due to these recent discussions, I'm going to add to the contruction manuals to clarify this stuff and to help people achieve the boat of their dreams as easily as possible.