Following Seas in a Gillnetter

One of the strange quirks of a gillnetter is that one must pull the gillnet into the boat and pick the fish out of the net. A stern picker like this boat might have a few issues with laying out and retrieving the net with a box bolted on to the stern. Apologies in advance for being a wee bit of a smart ***, but thought it might be pertinent to remember the primary function of this boat.

On another note entirely, what hull is that? The way I interepret the problem is like most little fishboats of this type it is balanced to go out nose heavy and come back *** heavy. Making the boat longer may just make the nose dig in deeper when running light.


Is this a problem mostly when traveling up and down from South east. It seems like you'd be running out with ice most of the time when fishing anyway. Seems like processers aren't as interested in warm fish as they used to be .

 

...A very valid point indeed...I had noticed the equipment back there, and am still mulling in my head the practicality of trying to reinforce the box enough to support the load of the equipment...thus, I must say that it was only my "two-cents worth," and not my "million-dollar answer" ... to be taken with a (rather large) grain of salt.

 

Robherc:

A friend has a narrow wooden boat from the late 1940s which had an 3'-4' aluminum stern extension added in the 1980s. Like TollyWally mentioned, they did have to move all of the stern gear rearwards in order to be able to fish reasonably well. So, Robbherc, your idea of a bolt on box can work, but the box needs to actually be built as strong as a new stern. The extension allows my friend's boat to pack 1500 or 2000 lbs more before the back deck goes under water.

Everyone at the time said that an aluminum extension on a wood boat was the dumbest thing in the world. It wouldn't work, it would corrode badly, it will leak at the seam, etc. etc. It seems to have held up fine. The boat is only a little over 8' wide and 40' long now. When the weather is crummy, his boat looks like a u-boat. He has the old style tiny wheel house which looks a little like a conning tower, combined with the narrow beam makes a wet boat. He goes through lots of waves, mostly you can just see his conning tower.

TollyWally:

It's an Albion hull, made in B.C. I think in Haney. Albion made at least two hulls, early ones had round chines. I've got the later one with hard chines. The boat is light in back whenever I don't have ice and fuel is down just a bit. If possible I run everywhere light (and get ice on the grounds) because the boat is faster. I like to return light also, having delivered on the grounds.

If the weather gets crummy I can tank one of my holds to keep the back end down.

re:tourists--you will need to get a tag.

 

Wow! Did he perform (or asked for) an stability calculation prior to that?

Cheers.

 

No, no stability test. I don't know of any older boat this size that has undergone stability testing.

 

Wow....

We perform a simplyfied stability test for small fishing vessels around here, like this:
- Boat in full load condition, this is full tanks, all crew aboard, fishing gear in its storage position (usually on deck) and an equivalent deck load to the pretended catch (or then in holds, but these boats use to carry catch on deck).
- Heeling weights given by the formula: W = 0,65 Afl (65% floatation area). You can estimate Afl as 0.7*Lwl*B for a typical boat.
- Weights are translated from B/3 at one side of the Center Line to B/3 to the other.

If the boat doesn't heel 14º nor submerges the deck at any point, then the boat has acceptable stability.

If not, load on deck has to be diminished till the boat complies. That will be the maximum allowed deck load to be safely carried aboard.

In my opinion, after having performing hundreds of such tests, I have to say the criteria provides a good level of safety. I dare to reccommend you to perform such a test for your boat.

Cheers.

 

In the 1960 ties it was named "Flettner Rudder" here in Europe, on the strange side of the pond I think just "articulated rudder" was and is the notion.
It will also allow to overbalance the rudder to about 35% (troublefree) to 42% let the manufacturer do the calcs.!!!!
Means you can come closer to propwash quite a serious bit. Altogether does´nt solve the problem but should let him stand the pain easier.
And here are the links:
Manufacture:
http://www.rudderpower.com/products.html
http://www.vdvelden.nl/rudders.cfm?pk=357&lang=en
http://www.turningpointmarine.com/turning-point-marine-articulating-rudder.php
Labba labba:
http://www.proboat-digital.com/proboat/200608/?pg=71
http://ducktalk.net/eve/forums/a/tpc/f/5621093711/m/2991080122

Just info (too big)
http://www.becker-marine-systems.com/

Cost is not too high.
I wish it would help, thats no job to play games with gear!
Regards
Richard

 

Guillermo,

The older wooden boat is my friends. His fishing cockpit is quite a bit lower than the main deck. He loads the boat till water comes in the scuppers in the cockpit, then runs to unload. He still has hold space available at this point. Obviously, the boat is over tanked. I would not build that much hold volume into a hull... But, ultimately he knows the issues with his boat and it's his problem. His family has managed to keep her upright for a little over 30 years.

However, your stability calc. is interesting. I get the part about moving weights B/3 to each side of the C/L. (ie. 4' on a 12' beam). I also think I get the part about the flotation area being 0.7(LWL*beam). What are the units of Afl and weight ?
Will 0.65 Afl work only in metric?

What do you consider adequate stability? Able to carry a full load in moderatly crummy weather?

Byron

 

Byron
I use those formulas in metric units, never tried in imperial ones, for which the necessary corrections should be done. If you use metres for beam and Lwl, you get the heeling weight in tonnes.

This system to evaluate small fishing boats' stability has been used in Spain at least since 1960, with satisfactory statistical results (accidents). An small fishing boat (less than 15 m LOA, let's say) complying with this requirement, is considered to have a low probability to suffer an stability related accident, if maximum loads used when the test are respected when operating the boat (although there's not a 100% guarantee, of course).

Cheers,

 

My 2 cents (tourist & french speaking tag!) suggestions:

1. Lateral surface center is too forward. When the wave pushes from behind, the boat rotates too easily around it.
2. Rudder bottom would be better if in alignment (lateral view) with the keel bottom, here it's shorter and rounded.

See picture (ok, perhaps a bit exaggerated, it's not a sailboat after all and rudder surface too big)

Possible problems: more heeling when running in following seas (the sea always comes a bit sideway). And with wind on your side, the boat might slowly turn downwind.

You say "I can tank one of my holds to keep the back end down" : does it help to helm with big waves from behind ?

and "Judging from the helm, the rudder is not well balanced" is this only a problem in the high following seas situation ? If not, it should be developped before any change is made to the rudder.

 

Chickadee,

The rudder balance issue is more apparent at higher speeds. The faster I go, the worse it gets. Following seas do not affect this.

When I fill a hold with water (or fish) the boat tracks much better in following conditions. Of course, it also plows more deeply into head seas when loaded.

RE the rudder size: At my annual haulout I will be increasing the size of the rudder a bit, adding rails or caps top and bottom and rolled "fish tail" sections to the following (back) edge. Other fishermen I have spoken with have been happy with these modifications on their boats, and it turns out that they are quite common on boats world wide.

I have often wondered why my boat is not solid down low the way you have painted in your retouched photo. I think that the reason is two-fold. 1, It's probably cheaper to use less glass; 2, it probably helps keep the rear end light for planing. I have 180 hp and do not quite plane (at WOT , but guys with these hulls and 400 HP can do 16-18 knots. I usually go 6 - 6.5 kts burning 2 GPH.

 

About the helm "instabiliy" at higher speed, some kind of profiled rudder should do better than a flat one. It's flat, isn't it ? Many here would have better words to explain that. Then again, a rudder as deep as the keel bottom line (my 2. point above) should really help to stay on the course, but in the present configuration it seems a bit complicated without cutting this protection behind the rudder "pivot".

The free space before the prop is great to make short turns - maybe important when working with the net ? but won't help to stay on course.

My idea was that the "keel" was steel, not plastic ! so it would have been easier to try some modifications, cover the space and weld a plate under the bottom, somethin solid enough to reinforce the rudder - and so suppress that thing behind the rudder : this curved support that runs behind your rudder can't be any good for flow, but to protect the rudder and that may be a tide and/or net issue !

Anyway, be sure not to weaken anything in this part of your boat! your idea of a "winged" rudder may be the best way to go. (although I don't get this "fish tail" sections thing on the trailing edge).

Good luck with your hard work !

 

Yep, that is a planning hull and the reason you skeg is open is to permit the disturbed flow, going around the skeg to "reattach" and calm down a bit, before entering the prop. Other wise it'll be sucking disturbed flow, which is much less efficient. Of course there's the additional drag issue, not a good thing on a boat that can plane.

Your end plate modifications will work well enough that you might be able to live with it without further additional cost and alteration.

 

There will be plenty of waterflow even with the keel "filled in" at twice, or more, the speed you are doing - just mind your taper (and try to clean up your flow everywhere you can). I understand the constraints of net-handling with a gillnetter (I have one, too) and I feel that your prop and rudder could easily be set another foot aft, a side benefit being that you would be able to swing a bigger prop if you chose. Steel plate rudder, wedged in the aft three inches to prevent flutter, top and bottom plate unless you want to get fancy - which just isn´t worth it at your speed. And you simply must be willing to tank down a little, minding free-surface area, for a following sea. Work fast to be ready for this season. Good luck - Mark

 

I've just now realized I made a gross mistake. It is 0,065 (6,5%) times Afl, not 65%.

Sorry.