Minimum Planing Speed

[starbright55]

I was out in some rough stuff last weekend and I was pondering how I would handle it in a GA.  Slow down is the obvious answer and I'm ok with that.  Current boat barely planes at around 17 knots has a 22 degree deadrise.

So the question is, how slow can you go in the GA, staying on plane?

I don't really know how to read this:
http://www.glacierboats.com/hydrodynamics.html
But my impression is that when the trim degrees "max out" at 14 knots (4.780), anything slower than that and you're "climbing over the hump and past that you're solidly on a plane.  Good guess?  I know that both the GA and Tolmans don't have much bow rise while accelerating and planing can be barely noticable except for the  increased reading in fuel economy.

The difference between 17 knots (in my current boat) and 15 knots in a GA doesn't sound like much of a speed difference and I know I still get beat up at 17 knots in my boat!

[Brian.Dixon]

You read it right ...Note that certain boats (Tolman Jumbo, Bluejacket, Great Alaskan) just sorta rise up onto plane without a noticeable hump to get over ...4 degrees isn't anything you notice in real conditions.  You can operate the boat fairly efficiently at 10 knots.... and you don't have that weird effect where the boat suddenly over-accelerates as it crosses the 'hump' onto plane, causing you to charge ahead way too fast into oncoming swells (usually popping airborne on the backside).  The Great Alaskan is a lot more controllable and lets you use the throttle to raise the bow a tad while climbing, easing off a tad down the backside, without the tendency to shoot ahead and cause bad slamming.  That said, your deep-V heavy boats (that burn twice the fuel) can generally go a little faster in the rough stuff.  One price that you pay for getting a lot better mileage in the GA is that you do have to slow a tad more when going through a rough chop.  It'll do it faster than a Tolman though, and has a finer entry ...you'll leave the Jumbo's behind, but the SeaSports will leave you behind.  .  But you can laugh at the SeaSports when you go fishing twice as often for the same dollars spent on gas... in a boat that cost you 1/3rd as much to have, brand new ('sweat equity' though).

Brian

[Dave Collett-Paule]

I've got over 100 hours on my GA and I've only felt the "hump" a couple of times in calm conditions.  It seems like 13 knots is the magic number for getting on plane, but once on step, throttling back in the chop, it seems like you can go as slow as 10 knots before you start pulling a big wake.  Just my observation.

[Brian.Dixon]

I've got over 100 hours on my GA and I've only felt the "hump" a couple of times in calm conditions.  It seems like 13 knots is the magic number for getting on plane, but once on step, throttling back in the chop, it seems like you can go as slow as 10 knots before you start pulling a big wake.  Just my observation.

Interesting how coming off step happens at a slower speed than going on step ...I wonder if that's typical for boats and i just never noticed?

bd

[starbright55]

Thanks Brian and Dave.  13 knots should let you stay on plane, plow through the wind chop, and not go airborne over swell!

Interesting how coming off step happens at a slower speed than going on step ...I wonder if that's typical for boats and i just never noticed?

Seems normal to me. my boat has a no-mans land of 1200-1800 rpm (displacement speed below, planing, above) and I can usually throttle up to 2000 to get on a plane and then back it down to 1800 rpm and maintain plane

[BobC]

My boat will be used primarily for trolling.  We pull planer boards for walleye and Stripers fairly slow (2-3MPH) but if I decide to do some high speed trolling for Wahoo offshore, trolling speeds could be up to 22 MPH or anywhere in between depending on sea conditions.  I will be on the light side of of a GA build and likely running no more than a 150 Etec or a 140 Suzuki.  I plan on carrying about 60Gal of fuel.  That said, is there a speed at which the GA's don't like to run or do they have a pretty smooth transition like the Jumbos?  What can I expect through the trolling speed range?  It seems like if you can back it down to 18kt. and stay on plane. I could theoretically do my high speed wahoo trolling on plane at a pretty efficient cruise.  That would be nice.  But what would I see at say 5-9kt range.  Does it shove a lot of water or roll along pretty smooth?  If someone could shoot a video of a GA going a variety of speeds through the planing transition for a few seconds that would likely be of big help to potential builders.  I know it would help me.  I realize every setup will very based on motor, weight, prop etc. but at least we would get a baseline.  I haven't found any youtube videos of a GA running.  If there are a few out there,  maybe someone could point me to them.  Thanks.

[Brian.Dixon]

I think Dave C-P in Homer can probably answer best - out of personal experience doing much the same thing - but note that the GA doesn't operate like the heavier glass deep-V boats do.  As it transitions to planing, it just sort of rises up and goes ...no bow-high weirdness.  Without careful paying attention, you may not even notice the transition.

Brian

[starbright55]

Bob, my comment in post 5 was about my current boat and a "no mans land" was for my current boat - not a GA. Brian says very little bow rise or noticeable transition from displacement to planing.

[Brian.Dixon]

Bob, my comment in post 5 was about my current boat and a "no mans land" was for my current boat - not a GA. Brian says very little bow rise or noticeable transition from displacement to planing.

According to the hydrodynamics modeling (cool, eh?), when the boat is built to 26 feet and exactly as I assumed  during the design process, the bow trims up by about a degree when at rest, about 2.x degrees during high speed planing (say 30+ mph), and reaches a maximum bow-up trim right before it goes on plane of about 4.x degrees ...not much change.  The bow comes down the faster you go until it's down to about 2.1 degrees.  Once you're within 20% of planing speed or so, weight distribution starts becoming far less important to trim compared to the planing forces on the hull.  One of my goals during design, specifically, was to NOT create a boat that stuck its nose in the air when trying to go on plane ...and anyone that's driven a boat that does that knows exactly why (not counting racing boats - a different breed altogether).  A friend of mine had one of those football-shaped SeaSwirls that ran like that ...everyone had to run forward to try to get the boat to get on plane.  It was a re-fit with a V8 that was a little too heavy for it, but the owner told me that the behavior was similar prior to the re-fit.  Boats that lift like an elevator onto plane are a pleasure to operate.  The only possible downside is that it limits the 'big water' technique where you use the throttle to hold the speed that keeps the bow at its max while you run into and climb the 'next big swell', then back off on the throttle over the top and let the boat sink back down into the trough with the water, repeat.  You can cross pretty heavy water like that if the seas aren't too mixed.  The Great Alaskan's high bow makes up for that difference, as do other seaworthiness features such as aspect ratio (efficiency and maneuverability), flared sides, relatively stiff when heeling (higher transverse metacentric height, GMt, makes the boat roll with the waves rather than allowing them to climb too high up the sides etc), relatively not too 'stiff' when responding to water that would raise the bow - driving into swells (moderate longitudinal metacentric height), etc.



Brian

[BobC]

Thanks guys, that is very helpful.  I don't want a boat that shoves water through the planing transition, goes bow high or digs a big hole behind it while trolling at higher speeds.  I have been there and done that and it takes the pleasure out of fishing and kills economy and handling.  It sound like I am on the right track.


 

[Brian.Dixon]

Thanks guys, that is very helpful.  I don't want a boat that shoves water through the planing transition, goes bow high or digs a big hole behind it while trolling at higher speeds.  I have been there and done that and it takes the pleasure out of fishing and kills economy and handling.  It sound like I am on the right track.

 

[davidnolan]

as a data point my Jumbo is about 10 kts getting up, the widebody 23 footer was about 9.

Bob what kind of lure can you pull at 22 kts.   That's screaming.  Last year saw many wahoo caught offshore and a couple of my friends got them.  We got whacked and cut off with a bally hoo and another new joe shuts bally head came up with the powder coat teeth marked into the head.

As another data point, I had Dave Shoemaker out last year on a 36 hour offshore tuna trip.  He had just got off the plane from Alaska where he fished with Daves GA.    Dave shoemaker reported that he really couldn't tell too much difference in the behavior of the two hulls, Alaska Daves GA and my (DAve N) 27 Jumbo.     Theres way too many daves in this thread.   I cant wait to get out in either Dave's (shoemaker, not Nolan or collete) GA or Bob's (Virginia) GA.

My 27 Jumbo is a whole order of magnitude bigger than the 23 widebody and so I imagine the GA will feel that much bigger yet again.  We typically run with 80-90 gallons of fuel (60 miles off, trolling up to 18 hours in the day and following day, and back, #300 of ice and #100 in bait, four PAX.   


Heres a picture of the skiff in the Lindenkohl Canyon about 72 miles off OC Maryland right after boating a nice YFT 

[BobC]

Dave,

They make highspeed Wahoo lures.  On a slower boat, some guys will actually drag them while running out and make good use of the burn time.  Never know what you might hookup on.  Here's a link to one type of highspeed Wahoo lure. You'll note the Banshee Supreme is for up to 25kts.  25kts. is actually a pretty nice comfortable cruise speed in my book.

http://www.ballyhood.com/html/wahoo_lures.html

Who took that picture of you out in the canyon?

Welcome to the GA party!  You will certainly be invited to take a ride on my GA once finished.

[davidnolan]

There was a guy named Alex whos friend was also going out.   He was there ahead of us and the folks were fishing for mostly Bigeyes into the dark and very early am.   I got the picture a day or so after we came back in.