Lengthened 1990 Hakvoort LRC; opinions please?

Of course the LCG it is aft of where it was on the ORIGIONAL HULL. But, you guys are responding to my post, which I origionally explained that putting a cockpit extension made the LCG too far foward and if you didn't have the boat trimmed correctly it would ride bow heavy and behave horribly in a stern sea. The LCG being too far foward for the boat to ride and handle correctly..... with no correlation to the old LCG the old hull or anything. The LCG too far foward for the only hull that matters, the current hull with the cockpit extension.

That being said. With just a cockpit extension, the LCG is indeed aft of the origional location on the origional hull, but not far enough aft for the new overall length for the LCG to maintain the same distance percentage from the transom to LCG as the old hull for the vessel to run with the same trim as it did before the extension. IE. the cockpit extension did not move to COG aft 10' to match the 10' added, not even close. It will ride bow heavy, and most naval architects balance that with fuel and water tanks, but as you drain them it again bounces the LCG further foward or too far aft if you have too much back there. Needless to say with a yacht with a cockpit extension you have to get very good at trimming the boat and where you draw fuel and water from.

In the 65' Hatteras I gave as an example, the origional fuel tanks were mounted right at the COG, so as they drained it didn't effect the trim of the vessel hardly at all. But now with the extension they are foward of the LCG, and the cockpit tanks way aft of the LCG, so draining fluid from any tank has a big effect on the vessel's trim and the ride and handling of that vessel. Get the cockpit too light and it rides like coming in an inlet with the trim tabs all of the way down in a following sea.

Stated earlier, that could have saved at least 7 pages of this thread.

Nope, in my posts I have said this all the time. The math and physics must of course be used in the new hull to establish the LCG. What happens in the old hull if you just add weight and don´t extend it is pretty obvious.

But you have to add a grain of common sense to the math. At one point I thought that Marmot have come up with something of interest, but no, it is just an endless rant trying to justify his original ironic post.

I know you feel strongly about your position, it is just not an apples to apples comparison of the before and after situation. Adding the extension and then changing the reference point does not allow the comparison to remain in the context of the reference hull (pre-extension). By doing this I did not see the same irony that you can not let go of.

It is no mystery that if the extension adds an additional amount of displacement, that it will be compensated by the appropriate amount of weight (outfitting) to float the vessel with a neutral trim (level) or back to the same condition as the reference vessel.

There is not much more to say on the subject matter, and I wish you continued success in your endeavors.

The juxtaposition of those two thoughts is more irony than I can stand.

Rants

Talk about endless rants.

What I read was Marmot was correcting the misconception by some that by adding an extension (weight) aft the CG moved forward.

CaptJ made some good points on the handling of any vessel when an extension is added but he should have stopped there. Obviously he has a lot of experience cleaning, maintaining and driving yachts but lacks technical expertise that numerous senior members on YF's have.

ie. changing pistons while the engine is running on a commercial ship was another subject that he talked about and wouldn't stop even when it was pointed out how ridiculous that idea was.

However even he seems to have grasped the fundamentals of naval architecture so I find it surprising that you are still arguing the point.

I would have thought that being a designer of yachts you would have and easily could have downloaded technical drawings showing us poor mortals what we are missing. As you stated it was one thing to start changing hand drawn plans but nowadays with a few key strokes on your computer you can change anything.

The "cartoon" drawings (sorry, another members reference) you downloaded showed me and I am sure most other members absolutely nothing.

You mentioned that the LCG is measured from the lowest point of the transom, can you tell me where that would be on say a fantail.

In the real world all measurements are taken from known fixed points, ie. rudder stock, an aft water tight bulkhead etc. however I will give you the point that even Feadship measures there 45 meter (semi-production) yacht from the lowest point of the transom but the majority of there custom boats it is measured from the aft bulkhead or rudder stock.

I have also to add that after nearly 45 years of working on ships, yachts and boats I have never heard of LCG, VCG etc etc being referred to as being a percentage from anywhere. I must have missed that class in the five years of university & college studying marine engineering and naval architecture. However if indeed you measure in percentage, I thank you for teaching me something.

Most of us with any experience down here in south Florida have seen a lot of extensions, mostly cockpit extensions will probably agree with CaptJ on his handling comments.

I just wonder how many extensions you have designed or have experience with plus I wondered why you posted drawings of a 1931 boat, firstly I thought you were saying that you had designed it but then thought how can a man of that age be so good on a computer.

As for the op, extending a yacht by inserting a section in the center or there abouts is the best case as far as handling etc but in practical terms most people what an extension at the stern, not always as a cockpit. Extending in the center which is normally the widest part of the body will add a lot of volume to the vessel. Numerous cruise ships have been extended this way to add a lot of cabins etc. it would look kind of odd adding a 30 meter stern extension with cabins stuck out there.

A lot of ranting going on here so maybe I can give my 2 cent worth.

In the real world the original vessel has a known reference point and very often is the centerline of the rudder stock,from there the various LCG, LCB etc are measured. Adding an extension (weight) will move the LCG aft, end of story at least for me.

Know what's ironic? Your drawing of the runabout has frame 0 at the bow.

The bottom line is a runabout or little boat doesn't need a stability book or an operator who can even spell stability. You have proven that you are free to call it whatever you want and it doesn't matter.

However, in the real world, large yachts and ships require a NA to document the locations of G and calculate the effect of changes including extensions. All changes are referenced from to the original CG and the original reference point because that is the way NAs and class societies work.

When an alteration is made that changes the location of the LCG more than 1%, class requires a new inclining experiment to document the new conditions of stability.

When a NA designs an aft (or any other) extension, he or she will calculate the weight and CG of that new item. That information is used to calculate the change in location of the LCG when the extension is attached. That calculation is based on the distance from the existing reference point whether it is the FP, the AP, or midship to the CG of the extension. It is not calculated from a newly developed location that never existed before.

If the change in LCG exceeds 1% then a new inclining test will be performed and a new or modified stability book will be developed. Neither the boat driver, the interior designer or the stylist will be involved in that process.

OK, so then your extended boat will need to have added weight forward to keep the LCG in the same relative position..? In my boat I would add that weight aft, as I consider the LCG to have moved forward.

The reason I showed the old drawing is that it was done by hand, as opposed to my drawings that are CAD since the mid 80:s...

About how many extensions I have made, I can say at least 100.000 in the computer and so far the LCG have landed right on those built...

Have you read post #121?

There seems to be a great deal of difficulty in understanding the difference between buoyancy, trim, and CG.

One could add enough buoyancy aft to submerge the bow but not move the CG one inch forward.

One could add a 50 ton extension aft and not change trim one inch either way.

J should stick to driving boats.

Whoa

Amazing, well I will take my hat off to you sir and obviously after 100,000 extensions you have much more knowledge than I will ever have. Between your experience and CaptJ's 15,000 miles per year for the last twenty years what the heck are we doing trying to explain things to you two for.

I would like to know where all those boats are with extensions though.

Maybe I should have asked how many have you designed and had built.

As I said, in my computer. Every design is tweaked in all directions thousands of times before settled on. All of them have centers of gravity moving accordingly in all directions at the same time. If I think the LCG is too far aft, I can extend the hull and then I expect the LCG to move forward, not aft...

That'll work. Keep extending it until the transom shows up on the horizon ahead of the bow and then it will be true. Pure genius.

Puts a new spin on the term "globe circling boat" as well.

You're splitting hairs again Marmot. Is a boat measured from the bow or from the transom???? The transom is always 0, so yes it does indeed move further foward from the transom if you move the transom back further, (in relation to the bow no, then it is aft but nobody measures from the bow)......Once the boat is extended, you can totally forget about the old hull, it no longer exists, it's permanently GONE. Under 100'< the transom is the transom.....not -1, -2, -3.....whatever. This is not a large ship or a megayacht, the ORIGINAL POST is in reference to a 1990 Hakvoort LRC where they extended the center of the boat, so the transom should still be referenced as 0, so yes no matter how you figure it, the LCG still moved further foward from the transom on that boat.

If the LCG is measured in distance from the transom. and is 20' from the transom on a 50' SF. Then if someone extends the cockpit 5' with not a lot of weight there and the LCG ( LCG does indeed move aft from the bow, but it's not measured in distance FROM THE BOW) will move further foward from the transom and now be say 23' foward of the transom. In real life, this will make the boat run flatter.
Are you an Engineer or a Naval Architect?

This is where the problem lies in almost all yachts 100'< with a cockpit extension. The weight that is added to float the vessel with a neutral trim with a cockpit extension is almost always a fuel tank and/or a water tank, not permanent dead weight. Tanks that lose weight as you use the boat. Draining the cockpit fuel tank before the rest has a HUGE swing on the trim of the vessel since it is at almost the furthest point aft from LCG. The normal boats fuel tanks/water tanks are further foward than the LCG now because you moved the normal LCG aft, so draining them swings the trim to the aft.......So the problem lies in the fact that as you use the boat there are HUGE swings on trim that greatly effect handling and can effect safety of the vessel. You have to be real keen at constantly trimming the vessel by means on compensating for fuel and water load changes.

For example if you're running the yacht at cruise with the watermaker going filling the cockpit water tank at 50 gph, but are drawing fuel from the normal boats fuel tanks foward at 80gph......in an hour at cruise, most yachts will have a huge trim swing to the aft.....You just took 560lbs from the bow and added 400lbs to the stern IN ONE HOUR.....multiply this over a few hours......If you anchor for 3 hours and everyone swims and 6 people take showers......again as soon as you get moving, you have a huge trim change.......many times negatively effecting handling.

Just this year so far, I did a delivery ft. laud to St. Aug 280NM, Ft. Laud to Corpus Christi. TX 1300nm, Ft. Laud-Key West-Naples 300NM, Naples-Marathon-Key Largo-Ft. Laud 300 miles. Ft. Laud-Nassau-Harbor Island-Exumas-Nassau-Ft. Laud 700nm. Pompano Beach to Jacksonville 300NM, Ft. Laud to Myrtle Beach, SC. 700nm? Plus a lot of 30-100NM day trips and it's been a slow year. I have 7 different yachts to load on freighters next week. 2 of those will be a 50NM run to where the freighter loads.

I've run probably almost 40 yachts in the past decade with you standing on them!

Too funny.


Then, again, will a new Thread appear debating Earth - flat or curved?


P.S.- Will some be ahead or behind the curve?

OK, so if the reference point is the rudder stock or aft bulkhead on this Hakvoort LRC as the reference point. If they did the extension in the center of the boat and the weight and extension was added foward of the engine room (majority of the weight of the boat, and most likely the origional LCG was somewhere in the length of the engine room), it could conceivibly move the LCG foward from it's origional point from the rudder stock or aft bulkhead, could it not considering the weight and extension was added foward of the aft half of the vessel where the LCG origionally was???

We know the answer to that already. The new discussion will be whether the hull follows a rhumb line or a great circle!

And then there is the conundrum of what happens if the boat is built in Singapore for example then sailed to Scandinavia. Would the bow trim up or down as it went north and passed its own stern?

Or if it was built in say, Hammerfest, Norway ... would it trim bow down or up as it moved south and the bow got further away from the stern?

Cg

Let me explain CaptJ, I am an engineer and we rely on our training and facts. Before agreeing or disagreeing with what you are asking I would need to know a lot more information. I would not open myself to ridicule on here by giving an opinion when I don't know a lot of required facts.

I often wonder why you don't sometimes be the bigger man and admit it when you are wrong instead of changing the goal posts. You may find you will gain a lot more respect in the future.

As for your miles travelled per year, by your own admission you have done 3600 plus a lot of day charters, 4th July, half a year has past so are we to assume that by the end of the year you will have done 7200 miles for deliveries and 7800 miles on numerous day charters.

Maybe it is a slow year but to state you have done 15,000 every year for the past 20 makes me think that there has never been another slow year in all those years.

Stick to what you know, your helpful hints about cleaning boats I am sure has helped a lot of members. In fact your comments about how the boats with extensions ride is about right however it is to encompassing as one member pointed out a 42 (I think) uniflite does not ride as a good as the 48. You state trim arguments on your experience with hatteras motor yachts, how do you change the trim on a say Viking that has 1600 gallons forward of the engine room and is used first plus a 260 gallon holding tank all the way forward that is dumped when offshore. May I suggest pushing those black buttons that control those little things stuck on the transom, sorry are stuck on point "0" at the transom while some are hinged further forward of the transom, yes forward towards the LCG.

Enjoy July 4th

I am not changing the goal posts, the entire thread started and is under the subject of this one Harkvoort LRC that was extended midships foward of the engine room.

If a boat rides/runs bow heavy or bow down, pushing those black trim tab buttons on the dashboard or pushing the throttles foward is not going to make it run with the bow higher, the only way to raise the bow is to remove weight foward of the LCG or add weight aft of the LCG. Without making major changes (changing shaft angle etc.) Now bow high is a different story, you can counteract that most of the time with trim tabs and/or more speed.

I origionally stated that I do 12-15,000 NM's each year and when you average my career, I indeed do. Not to mention have several 1,000NM+ trips lined up at the end of the year already.