View Full Version : outboard motor wells farther inboard?
09-09-2006, 12:21 AM
I have a boat I been doodling on for awhile to use with a 8hp outboard I have. To strike a balance between keeping the boat trim and getting good flow around her, I need to bring the motor well forward. I have seen outboard wells near the bow in seine netters but I never seen them close to midships. http://home.nycap.rr.com/richboat/boat13.jpg
I can foresee the steering response being sluggish. But I haven't thought of any other problems. Am I missing anything?
09-09-2006, 06:43 AM
That makes a lot of sense in some ways. I've seen s omething similar before--I'll try to recall where.
09-09-2006, 06:58 AM
Thats fairly common on launches that manuever other vessels into positioning such as old timey boatyards. They work great in small areas, requiring less radius.
09-09-2006, 09:45 AM
Rich, saildrives in many yachts configure like that. Not steerable usually.
But if you fitted a skeg/fin ahead of the well in yours it would give a pivot for the motor to turn the hull, not sure about the stabilety of the short couple.
09-09-2006, 02:36 PM
Rich, the well placement you drew is very close to what the 19' Bartender has - details are different though. Even at 32 mph it runs clean and balances beautifully. A properly built ob well doesn't need a tunnel to make the water flow smoothly.
Many have built ob motor wells positioned a significant distance forward of the stern, but I haven't seen any that perform better than what George Calkins designed for the Bartender.
Why not just mount the outboard out of way.
Like up front under the bow decking, should have more room then.
Look at the fourth boat down, a small pacific ocean salmon troller that has a well, up front under the bow deck. The motor pulls the boat along instead of pushing. I bet it would be very economical, probably only do 10 m.p.h. tops, sure don't have to worry about tangled lines. Might get some strange looks backing it in to the beach.
09-09-2006, 10:11 PM
This is very common configuration on small commercial boats (bay boats) on Chesapeake Bay. I don't know how well it works but I believe they do it this way so the nets won't get caught in the prop.
09-09-2006, 10:32 PM
We were fooling around with an electric trolling motor on a 16' canoe. We used a 2x4 clamped to the gunwhales so could move the motor fore and aft easily. With one person in the middle and the motor mounted behind him it was almost impossible to turn. Moving it aft to a few feet ahead of the stern, it steered fine.
I think the motor needs to be near the end, front or rear, to effectively steer. The clam farming skiffs I saw in Cedar Key, FL have the outboard right up in the bow in a well and work fine.
You could add a bit of lateral plane (a small skeg?) forward if necessary to improve steering. Maybe push the OB back and steer with a tiller extension or cable & pulley arrangement.
A piece of PVC pipe, hose clamped to the rotating (throttle) part of the tiller, makes a good extension. Paint it the motor color and no one will know.
09-10-2006, 08:17 AM
Your sketch is a duplicate of the 14' x 42" poly canoe I motorized. The well shape is exactly as I built mine. What has been said about turning is correct. I had to add some lateral plane forward of the well because I could get the boat to run sideways rather than turn. Also there is a standing wave set up in the well at any speed over 2mph that is very irritating as it sloshed from one end to the other. I finally ditched the 3hp Johnson and went with a 42# thrust electric. Built plugs to close off the well after putting the motor in place and it is a delightful ride. The plugs in the well raised the top speed from 4.2 to 4.4 mph at full throttle on the electric, indicating the unplugged well was highly inefficient. It really shows up when you only have 0.66hp to work with. 40 years ago I started a Bartender and never finished it. Don't remember the well shape, plans long since lost. Anyone know of access to the design on the web? I'm only looking to learn something not build the boat.
09-10-2006, 03:16 PM
Is why I mentioned the tunnel. It seemed it would help in the boat's tracking/turning,and relieve some of the wash in the well. A tunnel becomes a keel of sorts too.My only experience with this configuration is in the more foreward mounted well configurations of the local net skiffs here before the gill net ban.I was told that the tunnel not only enabled the boats to run very shallow but by default,resulted in a drier ride.
The net furling off the back of the boat allowed it to steer more normally when making a strike but other than that,the boats were quite maneuverable.
09-10-2006, 11:54 PM
Thanks for the replies. Over the weekend I checked out Sucher's "Simplified Boat building" from the library. There are sketches and offsets for several boats with motorwells near the bow. After some thought I am going to pursue using a bow mounted outboard. I like the idea of having nearly 10' of unobstructed deck and I am willing to give up speed for it.
The hull I have been working with is close to the bottom dimensions of Sucher's 17'6" seine skiff (page 298). I have a 1/4" scale model I made last week that I'll fabricate a motor well into next week. I'll add lead to simulate motor, fuel,driver and passenger to see how it moves in the water. http://home.nycap.rr.com/richboat/bub2.jpg
In Sucher's book he shows a motor well (page 299)about 40" long with a shallow slope to the rear of the motor well that he claims will reduce the sloshing and resistance , I am thinking about curving that slope a bit to see if it might provide additional improvement to the flow.
09-11-2006, 12:29 AM
You should have a lot of fume, I mean fun, with that engine position.
Well if you really do it, definitely report thoroughly back on this project. May be real interesting to say the least. I suspect you wouldn't need more then a 10 horse, maybe a saildrive outboard with a bigger diameter prop.
I kinda think like bill says, what about fumes. With a outboard that exhaust through the hub, and as long as you are barely moving, it may not be a problem, but maybe you don't want to sit still with the outboard idling. Might be a fun boat though, with some unique qualities.
09-11-2006, 09:43 AM
We just added some video clips on the Bartender site. These clips show a 19' Bartender doing its thang at various speeds - unadulterated fun!
No water intrusion from the well at any speed except at the end of the last clip where I swap ends (don't try this with any ol' boat) and take about 10 gallons of water over the side and up through the well. Once I accelerate out of the turn the water quickly drains itself from the cockpit sole through freeing ports in the sides of the well.
09-11-2006, 10:47 AM
:d :d :d
I thought that boats didn't have brakes!
Great videos and music. I have rarely wanted a motorboat more.
09-22-2006, 10:57 AM
Some Hamilton jet boats in NZ can stop in their own lengths, so the story goes. Just by dropping the astern deflector into the water jetstream, thrust is reversed and the boat stops like it's hit a brick wall. http://www.hamjet.co.nz/index.cfm/The_Hamilton_Waterjet/How_A_Waterjet_Works
09-29-2006, 10:04 PM
I did some testing, I built a 1/4 scale model first with the motor plate 7 ' (in scale) from the transom. http://home.nycap.rr.com/richboat/btm1.jpg
I expected the water to flow pretty well because I had a curved ramp on the back of the motor well. However the water flowing through the motor well would eddy(pump?) up into the motor well at slow speed and if I pulled the model fast enough it would splash over into the boat. http://home.nycap.rr.com/richboat/mtrwellt.jpg
I figured the way the rear motorwell had performed that placing the same motorwell near the bow had to be worse . I removed the motorwell from the model and moved it to 6'( in scale)from the stem
To my surprise the motor well mounted near the bow had almost no turbulence in the water flowing through the motorwell regardless of how fast I towed it .
Anone have an idea as to why the front motor well might have flowed better than the rear?
Neat and interesting.
I suspicion if I say this right, that there is less pressure. As you put the well further back, the water under the boat is being compressed downward, causing a upward pressure and turbulence.
That also exsplains why a outboard mounted further away from the stern on a outboard bracket works better, it is in less turbulent and pressurized water.
Being that the well is so far forward, there isn't yet the pressure build up....
Very neat, so what are you going to do now...build one of these far forward well boats? It should take very little horsepower to pull a boat along at the upper end of the full dissplacement speed.
--additional thought- If the outboard was mounted under the bow in a well, you would almost have to use remote controls, unless you could turn a small outboard around and run it in reverse with the tiller towards you. Don't know if this would work right. ....But going back to your original drawing showing the outboard just aft of center, with your center seat being maybe a little circular so you can turn sideways comfortably, like in a little sailboat with the tiller.. Then to stop the turbulence and splashing of such a arragement, If you exstended the well all the way to and through the transom the problem would be solved and run smoothly with out the sloshing inboard of water. You could have a hinged lid over the well that would also serve as a sideways seat. Should make for a pretty neat arrangement for a flat bottomed skiff that is very simple and economical to use, actually user friendly. But also the thickness of your flooring, from outside bottom of boat to inside of top of floor, will determine your seat heigth. A thick bottom means that you need to go to a 25 inch shaft outboard instead of 20inch so the tiller handle is above the seat heigth....You can only have about a 4 inch thick bottom to use a 20 inch shaft and still maintian about a 16 inch seat heigth..
after that you have to either lower the seat or increase to a 25 inch shaft..
09-30-2006, 09:35 AM
Your theory might be right. I had thought that the upward pressure on the hull would be equal over the entire waterplane.
I also thought that because the front motor well is forward of the bottom's curve that it would act more like a scoop while the rear motorwell being on the back side of the bottom curve would have a slightly larger area to push the water out. I guess Harry Sucher and those Florida mullet fisherman know what they are talking about after all.
I don't know if I am going to build it yet or not, I need to
make another model with more bouyancy forward so the
trim is right and see how it flows again. I also plan to make a model of Suchers offshore trolling skiff (pg301) and see how the two compare.
09-30-2006, 10:31 AM
Using a tunnel to get rid of the turbulence is an easy solution to the turbulence problem but then I no longer have a flat deck at the transom (unless I raise the deck)
What attracts me to the forward motor well idea is having a 9'x 4'-5' unobstructed deck right up to the transom. I could load the kayaks on the deck and explore some of the creeks and inlets that are often too far to paddle to on a day drip or are unaccessable by land. Camping? I have a 3 man tent that would fit on the deck. Fishing? plenty of room for whatever I want to do whether it's line, net or pots. A boat version of a pickup truck?
What little information I have found on the mullet skiffs is that most have remote controls so the motor well is pushed as far forward as practical.( about 4' behind the bow) so it is pretty tight trying to walk around the motor. I am moving it back to 6' so there is room not only in front of the motor but around the sides also. I agree with the side seat idea it would be more comfortable and offer more leg room.
I haven't gotten far along enough to work on accomadations, I have a 20" shaft and the floors will be 6" so I may have to trade motors or make a small tiller extension to compensate
Speaking of motors, using the calculations in Gerr's propeller book I should be able to wring 6 knots out the 8hp motor I have depending of how much the well slows it down
Thanks for the advice
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