Opinions? (flatbottom skiff)

[duluthboats]

This is from another site, but think it's worth discussion.

http://media5.hypernet.com/cgi-bin/UBB/ultimatebb.cgi?ubb=get_topic;f=2;t=001614

100 hp for a 19' skiff?

Gary

[trouty]

Why not 100 hp on a 19ft skiff Gary?

http://www.fishingworks.com/Users/UserFolders/trouty/PhotoImages/sumpunt.JPG

Heres 200 hp on a 17 ft skiff!

Horses for courses...all depends on where your operating it- how fast you want / need to go and fuel considerations etc.

I have heard a rumour of one smilar to the above that came unstuck on a Downunder Northern territory river while negotiating a bend, seems the outside sponson dug in and it flippped..at about 70mph.

Seems the baramundi fishing occupants were thrown clear (into the crockodile infested river) while the craft skipped/flipped a couple times - hitting a riverside paperbark tree on the bank about 15ft above the water.

According to my scource - it's still there, neatly folded into a tight "U" shape around the sturdy melaleuca tree trunk!.

I'm told the crew got away with a fright , a dunking, some cuts n bruises, and were picked up soon after by another boat before the crockodiles made lunch out of them!

They would sem to be fine going in a straight line - corners may prove to be more of a problem however!. ;o)

Cheers!

[Willallison]

I guess it all depends on where you intend to operate and how fast you plan to go.
Raymond Hunt did't invent the deep vee because he thought it looked good - the simple fact is that if you want to go fast in rough water (with the possible exception of wave-piercing designs) there is little that compares to the deep vee. If the boat leaves the water, a flat bottom will always slam more than a vee bottom. The way to overcome this in a flat bottomed boat is to slow down - this is made possible by the fact that they tend to be able to hold plane at lower speeds.
As for the 100hp required, the photo and description of the skiff in question seem to indicate that it is very heavy - you only have to look at Tom's boat, "Liz" to see a boat in this size range which can manage to achieve almost the same speed with 50hp.

[Willallison]

Another thought..... if the boat were to be used to carry heavy loads, then 100hp, with a low pitch prop, seems quite reasonble.
Fishermen here often use 16 - 17ft aluminium dinghy's with tiller controlled 90hp o/b's

[duluthboats]

LOL!!! trouty,
Your clients must all go home happy. I started this thread with you in mind. ESP? Actually my first vision was of you in this guys boat, big grin on your face, a compass duct taped to the seat next to you, hand held GPS on a cord around your neck, and your hand on the tiller of a 150hp Black Max. The clients are strapped into lawn chairs amidships. The boat is riding on the top of the waves. LOL!!:eek:
OK, enough fun. What Brad on WB forum has is a dory skiff. Or at least that’s what I would call it. Tom has got me so wound up about flat bottom hulls; I’ve read everything I can find on them. Then you come looking for a boat that has everything. Well you’re not going to find it. BUT! Take a look at Brad’s dory skiff. He even has a window in the bottom.:D You take his boat, add 6’, add a center console, add some of the other stuff you wanted. Skip the tuna tower. Skin the bottom with a sheet of UHMW plastic. You won’t win any races with it, but it should get least 25 knots with around 120hp or less. This is an easy to build craft that will get you there and back. And it won’t break your pocket book. And that my friend is my opinion.
If you want to read more about them try Building Classic Small Craft, by John Gardner, or The Nature of Boats, by Dave Gerr. Dave’s book has a picture of a 28’ center console dory skiff. If I was looking for plans he might be a good place to start. I can’t find anything on the net. Maybe someone else has a link to some of his work.
Gary

[duluthboats]

Yes, it sounds as if he loads his boat down good. So he needs the hp to move the boat along on plane. What happens with all that power when he gets down to displacement speeds? Something else I would like to know, is this a time where twin engins would be more effective? Not for saftey, but run both at high speed and one for slow running. Is this done, if not, why?
Gary

Is this a time where twin engins would be more effective? Not for saftey, but run both at high speed and one for slow running. Is this done, if not, why?
I don't understand what you are thinking of - you mean having one 200 hp outboard for running fast and then one 40 hp outboard used for displacement speeds?

[duluthboats]

I was thinking of using twin 50's, instead of a single 100. Operateing one of the 50's at slow speed would be much more efficient. The unused motor could be tilted up. Does this idea have any merit? Other then initial cost and a little weight gain is there a down side to this setup.
Gary

[Willallison]

There are pro's & cons to what you suggest. 2 x 50hp motors are not as efficient as 1 x100hp, so the fuel consumption at speed would rise. However, you enjoy the benefits of two propeller in the water which gives more 'bite' and better slow speed manouverability, not to mention the safety factor which comes with redundancy.
At slow speed, the 50 should use a little less fuel than a 100, and certainly less than the 2 x 50's, but from an economy point of view, I would have thought that it would be better to go for 1 x 100 for high speed and 1 x about 15hp (with a low pitch prop to give good thrust) as a trolling motor and as an auxillary

Would you want to run with one engine only with it being off-center?

I bet the extra maintenance costs of twin 50's not to mention the extra weight would be more than just paying for the gas to run the 100 at slow speeds.

Anyone have fuel curves?

[tom28571]

You would only want to use one of a pair of engines for trolling at low speed. For running faster, the other engine would create a huge drag and needs to be raised which would give steering problems if they are both rigged on the same cable system.

If you are looking for safety in redundancy, a single large engine with a smaller, get back home, engine on a separate fuel system is a cheaper and more fuel efficient solution. Some people use the small engine for trolling and steer with the larger one with great fuel savings. It would be better to raise the big one and have the smaller one set up for steering but, hey, it works.

Since this thread started on flatbottomed boats I'll kick in a nickels worth (inflation). When the use of the boat calls for it, a flat bottom boat can be the best solution. Launching off a beach, working in very shallow water or using the boat for working crab traps and such are a couple of uses that come to mind. For almost every ordinary use, a V bottom hull will be superior in every way. Rides better, handles rough water better, is drier, turns better, tracks better, is more seaworthy, structurally stronger and has less tendency to porpoise, to name a few advantages.

[duluthboats]

You know Tom, I was hoping to get some help here from the audience. The fact that I didn't, must mean they agree with you.:)

"For almost every ordinary use, a V bottom hull will be superior in every way."

In my limited experience, I have seen that all planeing hulls have some bad habits. Your statement might be ture for boats that are being sold today. I think a flat bottom hull could match a V bottom if designed right. You might not find a market for it, but it would perform very well. And that takes me back to the price of dock space driving boat design. :D

I'm also sorry to tell you that I can't make it to the boat show. :( I was looking forward to meeting you and seeing your boat. You might put a plug in here and let people know about it.

Gary

[trouty]

I bin a busy boy so a bot late gettin back to check out the threads here! ;o)

Is it just me or does Gary's link above to the skiff details not work for everyone else too?

I don't really know what boat your discussing for the 100 horses!

I just threw in the 17 fter to show that 100 is probably not over the top...depending on where you operate and how fast you wanna get from A - B and whether or not going around corners is important. ;o)

Gary - your vision of moir at the tiller helm of the steelhead maru wearin my handheld garmin gps isn't that far off! ;o)

That said - she's still been 60 odd nautical mile to sea with moir doin just that - but SOME guys would do anything for a fish! LOL LOL

Sooo - Gary - you think 25 ft of flat bootom skiffs the go eh?...

Hmmm, maybe alink to my wave bouy might show the folly of that assumption....sure for the flatwater it's be great, but remember - this coastlines much like the one on the west side of Will's Tassie island.

This one swallowed a LOT of dutch east indiamen, and not just coz they were running ahead of the roaring forties and forget to turn left at Alberquerkie! LOL LOL

Noo - this is a nast bit a water at times...one of the nastiest....so whatever I get has to be able to take some serious punishment as well as the flats stuff...

Ask Will what his west coasts like - I think theres a lot of pro fishing vessels gone down on the west coast of Tassie - just as there is here!

Yeah - OK - all oceans get mean at times - none get meaner than ours.

Will - you explain it!

Cheers!

[tom28571]

Hi Gary,

I wondered if anyone would react to what I said about flat bottomed boats. We are mostly amateurs here and prone to falicious (is that a word?) beliefs based on limited experience and experience. I've also done a fair amount of reading on the subject of attributes of different hull forms which greatly influences my prejudices. Not to worry if my views are different from yours.

Nevertheless, I think my views on flat versus V bottoms are shared by most designers. My own experience with both types also support that opinion.

<<<. I think a flat bottom hull could match a V bottom if designed right. >>>

I have to dissagree Gary. In some applications, the flat bottom will serve a specific purpose better than any other but for most general use, I think the V is better in the areas I mentioned. It would be interesting to discuss any specific among those as to why one is better or inferior.:D

[trouty]

Gary,

I managed to get a look at both the link and the photo of his hull.

Maybe the other forum was just down at the time I looked at it before.

An "interesting" design indeed....

Still trying to make up my mind if the guys a genious or a nutcake? ;o)

Typical aerospace folks - think they know more than naval architects about boats, I wonder if he has input on commercial aircraft design...If he does, I hope I never have to ride in one! ;o)

A steep sided. flat bottomed boat with a canadian canoe type "rocker curve" built longitudinally into it...

I guess maybe it'd work - however, I'd want to operate one for a while first to see just how!

I think maybe the HP it uses is to overcome basic design flaw myself! ;o)

Who knows - maybe he is a genius...maybe one day it'll be a design concept adopted by many many boat manufacturers?...

Can't say the shape "excites me much" tho....

To each his own I guess......A wicked thought occurs to me tho...based on Garys vision of me at the tiller of a 150 black max, just gets my juices flowing!

Sooo - any ideas how I go about fitting tiller steering to my preferred power solution?

http://www.fishingworks.com/Users/UserFolders/trouty/PhotoImages/Gofast.jpg

This should bring my guests home with a serious grin on their dials! :D

Ohhhh yeah baby....I can see me now! Capt go fast trouty at your service!

Cheers!:D

[tom28571]

Trouty,

I don't see anything really outlandish in Bradley's flat bottom skiff. As you should know by now, I'm not a fan of flat bottoms but they do have their uses. There is no apparent rocker in the after planing portion of his hull and he does say that he avoided rocker in that area. Some of the rest of his characterization of his boat may just be a failure to comunicate just what he is actually doing so that we can understand it.

Some people have a much higher tolerance level for banging around on the water than others. How else to explain all the interest in wave jumping in PWC's and the like. Heck, in my salad days, I used to do this crazy stuff too. Nowadays I like a boat that treats my body with more respect, thus my favor for easier riding hulls than the flat bottom can afford.

As for the aircraft structural thing, almost all my boats have been built in the monoque "aircraft" fashion so it's certainly not new. When strength to weight ratio is important, that is the best way to build a boat. Of course, flat panels do not benefit from monoque methods very well and he misses the "boat" there.

Some people have the ability to visualize physical phenomena without understanding any of the math or accepted theory behind it. Maybe he is one of these. I am about half way between these extremes. I use the math and theory when I can absorb it but also try to think like a water molecule as it runs into the hull of a boat I'm designing.

[duluthboats]

Thinking I could continue this debate, I spent much time trying to dig up some support for my ideas. Instead I found stuff like this.

“There is a joke about the three most-often-told lies. To them I can add a fourth: that a flat-bottomed skiff will ride softly if its bottom is very narrow, or is turned up in front, or is built this way or that way. In any discussion of how boats ride, you must remember that external factors, such as speed of the boat, the height of the waves and their direction, and how heavily the boat is loaded, are at least as important as hull design. Since some of these factors can be controlled by the boat’s operator, evaluating a boat’s ride is complicated and subjective, and no aspect of boat design is more controversial. Perhaps I can say a vee-bottomed Tolman Skiff rides reasonably well if speed is reduced in rough seas. I can say with more assurance that its ride is a vast improvement over that of any skiff with a flat bottom.” ( Renn Tolman, A Skiff For All Seasons)

Renn has built both and he uses what he builds. With him and Tom agreeing, I would be foolish not to listen. I’m still learning, I hope others are also. Why else would I be here? :)
Gary

[tom28571]

Gary,

I've read Tolman's book and agree that he relates a lot of common sense in it. His method of construction is a little off-beat to me, but that means nothing if it works for him and his customers in the difficult areas where they are used.