Following Seas in a Gillnetter

[moose60]

Hello all,

I have a 36' x 11' gillnet boat that I fish in Southeast Alaska and Puget Sound. Over all it's a good boat. It packs around 12k lbs of salmon max and handles fairly well in most conditions.

My question regards following seas. When the boat is light, no fish or ice and less than full fuel tanks I have a tough time keeping the thing pointed in the direction that the waves are traveling. Hand steering or autopilot produces the same wild yawing. If I add weight the boat will track straight, but I push more water and slow down. I usually make 6-7kts @ 2 GPH .

I'd like to keep the boat light and be able to track well. Judging from the helm, the rudder is not well balanced. I have the space to increase the size of the rudder, esp. forward of the pivot. I would also like to change the rudder profile. If you look at my rudder from the stern now, it looks like an " l " . I want to box the rudder so that it looks like " I ". This has helped some other boats in the fleet.

Anyhow, I've attached a photo of the boat. Any suggestions are appreciated.


Byron

[PAR]

Putting end plates on your rudder will help steering response a little, but the wandering butt syndrome is a function of the hull type and not much can be done without very major surgery.

This happens because the beam is carried aft to the transom, which offers more hull volume, but also screws up stern too handling unless she's got a healthy load on. With some taper in her stern quarters, this would be much less a problem, though stern waves will still try to manhandle that broad transom.

The "downeast" fishing boats so loved by the yankees in the northeast, had nicely tapered sterns, but then some wise guy, got the brilliant idea of increasing hull volume aft, so a few more tons of fish could be carried. This happened at the end of the 1950's and it ruined the handling qualities of this hull type. Eventually it was figured out and the hull shapes went back to properly shaped quarters, but it seems not all designers, learn from this historical lesson.

[tom28571]

There is too little attention paid to handling downwind in waves. I see many powerboats with chines that run straight aft to the transom at maximum beam. This is guaranteed to make downwind handling more difficult if not downright dangerous. As Paul said, this is usually the result of a desire to get the most volume aft to carry load or support large or multiple engines. A taper in beam of 15 percent will improve things but is not an option to an existing hull. I see boats designed by people who should know better with straight chines. Many of these get away with it because they have huge and powerful outboards that don't so much as solve the problem as trample it to death.

The basic problem is that the water passage over a rudder is minimal with slow speed and the additional forward motion of water in the waves. A following wave hits the transom at some angle off center and starts to slew the boat around. Unless corrected by effective steering, the boat can broach or even capsize. Even if it doesn't do that, it can be hard work for the helmsman and no fun at best. Outboards are much better in this situation because steered power bursts can correct a course far easier than deflected water from a screw of an inboard.

One possible solution is a more effective rudder that deflects water better, especially at low relative flow speed. Such a rudder is shown by Dave Gerr in the August-September issue of Professional BoatBuilder. It is the Maclear-Thistle rudder. This rudder has flared trailing edges which generates much more lift at small angles for better control at slow speed. A modification to an existing rudder would not be too difficult. Adding fences will also help, especially at large steering angles. If you don't have access to that issue, send me an Email and I will run a copy and send it to you.

[rasorinc]

This is just to remind us all the dangers of the north pacific and how stability problems (over loading) can lead to many deaths.
http://www.oregonlive.com/news/index.ssf/2008/12/oregon_dungeness_exact_a_deadl.html

[Fanie]

Simple question Par,

How would two keels, one port and one starboard, if added, effect the handling when it's not loaded ?

Maybe stretch the aft third of the hull.

[moose60]

Tom,

Thanks for the info. I believe that I have seen rudders like the one in the article you mentioned. I can probably get a copy at the library. The ones I've seen have small wedges on the trailing edge. A friend recently told me that he was happier with his steering after adding two rolled "ramps" to the rear end of his rudder. These function just like the wedges, but perhaps allow a bit smoother flow/ vector the force more effectively.

PAR,

The boat has about a 1' taper from just behind the house to the stern. I have heard folks say that the closer a rudder is to the stern the better a boat like mine will handle following seas. I can't move the rudder because it's very nice to have the wheel and rudder tucked under the hull away from the net. Besides, I'd probably need a longer shaft, and a new strut.

A year ago I entertained the notion of adding a couple feet to the stern and increasing the taper dramatically. The idea fell by the wayside, partly because any addition would push the rudder farther from the stern.

so, (in you folks' guesstimation)

1. What would an addition need to look like in order to show a handling improvement?

2. Would a 2-3' addition give me more speed for a given power input? Or would the added wetted surface cancel any gains from a longer WL?

[PAR]

Fanie, his boat already has a substantial amount of lateral area, Adding more will just encumber it with more drag. Stretching the aft portions of the hull will not solve the issue, which is the huge hole it's dragging in it's wake, because the beam is carried all the way aft.

I'm just guessing here, but if the beam of that boat is 11', then the transom beam would likely be on the order of 9' 4". This provides a nice taper to the chines and helps fill in the hole, so the rudder can operate in less disturbed flow. Of course with any well immersed and broad transom, there's going to be some suction aft of the transom, but you can limit this to a fair degree with taper in the plan forms.

A few different rudder configurations could help her to some degree. Tom has mentioned some and you may want to look up the "kitchen" rudder too.

It might be possible to put an extension on the back of her, but I think you'll need a good bit more then 3' in length to do any real good. If you're running 6 - 7 knots on an assumed LWL of 33', you're running at 1.15 to 1.2 S/L. If the boat was 3' longer you'd only gain about a quarter of a knot in speed at the same S/L ratio.

Make the rudder top as close to the hull as you dare, which will serve as an upper fence and weld on a lower fence. Square up the shape of the rudder, so the trailing edge gains a little extra area in the process (the bottom too) and lastly consider adding some wedges.

[tom28571]

Tom,

so, (in you folks' guesstimation)

1. What would an addition need to look like in order to show a handling improvement?

2. Would a 2-3' addition give me more speed for a given power input? Or would the added wetted surface cancel any gains from a longer WL?

1. I can't tell, but handling improvement is not guaranteed by lengthening the boat.

2. Adding a little length won't increase your speed or improve handling very much though and surely not enough to justify the cost. I'd do the rudder thing first.

The waterline aft does look like the boat is dragging a hole behind the transom. It would take a lot of added length to bring the bottom up enough to get rid of that.

The rolled edge you mention is the same as the rudder I referred to, not flat angled wedges. this would be an easier mod than anything else I can think of.

[Fanie]

Sorry if I created the wrong impression.

The keel is large while the stern area seems flat. In my mind it is going to act like a forklift in following seas with the prop and relative small rudder to do the steering, hence the stern being pushed sideways easily.

The idea would not be to lengthen the boat, but if a keel is added both sides of the prop, won't that keep the stern from tending to get pushed or throwed sideways so easily ?

[PAR]

If a double ended stern was added, it might help considerably. You'd gain some volume aft to help hold up the stern and the quickly rounded stern sections would help split following seas, rather then resist them. It would place the rudder in better flow, but not in an ideal location for steering leverage (it would be better at the aft end of the hull addition, ditto the running gear).

Additional skegs wouldn't help Fanie. Following seas will grab the transom, lift it up and toss it to one side or the other, depending on direction from which they came. No amount of additional lateral area (skegs or keels) will prevent this. More lateral area (new skegs) will slow down the movement a little, but not enough to warrant installing them.

Substantially increasing rudder area probably isn't a good idea. When the rudder is in the prop blast, it has to be relatively small or it can get over powered by the wash. Ditto additional balance in the blade. The rudder appears to have about 15% in it now and I wouldn't increase this at all, as it's just under the amount I'd consider maximum for this arrangement.

Considering the costs associated with adding a double ended stern compared to increasing rudder efficiency, you're much better off with rudder modifications.

One other rudder modification that should be considered is a trailing edge flap. I'm not sure what it's called (some one help me out here) but the flap, which typically amounts to about 15 to 20% of the total area is the articulated portion of the rudder, while the rest is free to move with current and prop wash. It dramatically eases the effort needed at the helm and can "steady" her down a good bit. Of course this means a redesigned rudder and related gear, which is more costly then some end plates and other modifications.

[Guillermo]

There are not many (reasonable) things that can be done to correct the broaching tendency in a following sea for such a hull. I'm with Paul and Tom about just trying some redesign/type of rudder to improve its efficiency, with end plates being the cheapest/easiest solution.

moose60,
I see you have what I think are stabilizing paravanes installed. In what conditions do you use them?

[Gilbert]

Go to metalmarinepilot.com and click on publications, then download a pdf file of the paper titled "Rudders". Then download a form called "Vessel Eval" which, after you fill it out and send it to them, will supply the folks at Metal Marine Pilot with the information they need to give you a free optimizated rudder layout for your boat. The optimized rudder may not solve all your problems but it will certainly improve the steering and give the autopilot a better chance to do what it is supposed to do.

[moose60]

Guillermo,

I use the staybees when the weather is crummy. Generally 25kts or more and working the net. We spend alot of time laying in the trough. These make it easier to work on the deck when it is windy. You do have to be careful not to get 'em caught in the net. I almost never use them when running because they cost at least a knot if both are in the water. But they do work quite well when running.

If I know that it will be nasty I'll drop the poles early but leave the staybees on the boat. The poles can be tough to handle alone when the boat is really bouncing.

A cousin asked me how I like fishing where I do, I said "it's ok". He had fished the same place for 10+years. He laughed and said, "yeah, sure, it's fine. You just have to keep all the windows closed so that your stuff won't fly out of the boat."

[Guillermo]

Risky job! :)

Cheers!

[robherc]

Tom,

so, (in you folks' guesstimation)

1. What would an addition need to look like in order to show a handling improvement?

2. Would a 2-3' addition give me more speed for a given power input? Or would the added wetted surface cancel any gains from a longer WL?

Hmmm, I'm by NO MEANS an expert here, but it seems to me that you could fairly easily design a "bolt-on" box to bolt to your transom & add some much needed bottom-up, and sides-in taper to your stern. If you made it about 11"x3' at the front, and tapered it to, say, 9'x2.5' that the back, and say 2' long, I'd think you'd gain substantial handling in following seas, and with very little cost in terms of speed (if not a SLIGHT improvement).
If you filled your box with flotation foam, you'd also be tilting the balance of your boat a bit towards the bow...would raise the stern a little more & provide a little extra buoyancy, but I can't recommend it, not knowing how that'd affect your overall handling. I, personally, would be tempted to make the box waterproof inside & out, then drill a couple 1" holes in the bottom & top, let it fill with water, so it'll improve your handling, without affecting the fore-aft balance of your boat. ...it should also be (fairly) cost-effective to make, if you made it yourself.

Just my two-cents worth. Like I said, I'm not an expert (yet, at least)

[TollyWally]

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 ass, 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 ass 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 :).

[robherc]

...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. ;)

[moose60]

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. :)

[Guillermo]

..The extension allows my friend's boat to pack 1500 or 2000 lbs more before the back deck goes under water.
Wow! Did he perform (or asked for) an stability calculation prior to that?

Cheers.

[moose60]

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

[Guillermo]

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.

[apex1]

Considering the costs associated with adding a double ended stern compared to increasing rudder efficiency, you're much better off with rudder modifications.

One other rudder modification that should be considered is a trailing edge flap. I'm not sure what it's called (some one help me out here) but the flap, which typically amounts to about 15 to 20% of the total area is the articulated portion of the rudder, while the rest is free to move with current and prop wash. It dramatically eases the effort needed at the helm and can "steady" her down a good bit. Of course this means a redesigned rudder and related gear, which is more costly then some end plates and other modifications.

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.:D
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::confused:
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

[moose60]

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

[Guillermo]

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,

[Chickadee]

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.

[moose60]

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.

[Chickadee]

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 !

[PAR]

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.

[mark775]

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

[Guillermo]

- Heeling weights given by the formula: W = 0,65 Afl (65% floatation area)
I've just now realized I made a gross mistake. It is 0,065 (6,5%) times Afl, not 65%.

Sorry.