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THE LONG TAIL MOTOR

Posted by sean on November 28, 2010 at 9:00 AM

THE LONG TAIL MOTOR

by Sean Walker

The Asian long tail set up is by far the best; they were invented here and have been well proven over many decades. They can last years with almost no maintenance. The Western setup isn’t as good and they cost a lot of money. If you want to vacation in Thailand, you can take the important parts home in your luggage. These parts are very inexpensive. However, you can construct the long tail set up for very little money if you are up to the task. The following is a description of a long tail setup. It is not a plan but there are a lot of questions answered so it is helpful. A proper design would be desirable but there are not any available.

 

THE ENGINE MOUNT

 

When building a motor swivel mount a lightweight one is desirable. Make it simple, strong and use as little metal as you can to conserve weight but don’t go too light or it may not be strong. Use ring mounts for the tiller handle to slide into also. It has to move up and down 30 degrees depending on the transom height and left and right at least 60 degrees in each direction.

 

Hands off operation is the goal. This means while under motion if you remove your hands from the tiller the tail does not raise or fall but the boat runs along as desired. If this balance and thrust angle is not achieved it is too tiring to operate the boat, you will struggle to keep the prop at the correct depth and the boat will perform poorly. However, when sometimes going upstream or in rough water or at high speeds, it is still necessary to sometimes pull up on the tiller.

 

The mount must be balanced out weight and thrust wise to facilitate the tail riding in the water at the desired depth. It is very important the tail be about seven feet long (about 2 meters), and the engine be as low as possible. A short shaft will cause too much of a shaft angle between the engine and the water. You want the shafts angle not to be very steep. A nearly parallel attitude would be ideal but the shaft would be very long and the engine very close to the water. A good compromise will suffice. Mount the engine as low as possible. If your transom is high make a longer shaft.

 

When the shaft is fairly close to parallel to the boats attitude the turning and the power distribution is good because the thrust travels from the prop straight up the shaft to the pivot pin and then pushes the boat straight forward. If the shaft is at a steep angle the thrust power will not be used effectively. This is not like an outboard motor where the angle can be considered trim. When the angle is great the thrust pushes forward and the tiller handle pivots down, then you must pull up on the tiller or the prop will rise out of the water. However, you don’t need to understand this now, just keep the shaft long and mount the engine as low as possible.

 

You will need to find the balance point where there is the right amount of weight at the propeller. To find this fulcrum point, place the engine attached to its mount plate on a low table that simulates the engines height when it is mounted on the boat. Next place a piece of angle iron under the engine that simulates the pivot pin balance place. Then place a weight scale under the tail at the propeller. Move the angle iron balance point back and forth until the scale reads 6 Kilos (13 lbs). This is the point where engine pivots up and down so drill three or more pairs of holes into the mount so you can move the engine back and forth from this pivot point to fine-tune the balance after you test the boat. Be advised, heavier and more powerful engines require more weight at the tail than 6 Kilos, if need be drill more holes.

 

THE HUB

 

You will need a welder, pipe and some plate steel to make the hub. The hub bolts onto the engine and has a ball bearing inside it that rolls the shaft. Use an appropriate size pipe and an engine mount plate to bolt the hub to the engine. Drill two holes for the grease can or automotive type grease fittings. Small construction engines 5-13 hp. rotate at a maximum of about 3,600 rpm. Use a high quality bearing that suits your engines rpm.

 

THE SHAFT

 

As far as the shaft goes: the outer tube is often made of galvanized water pipe and has an inside drive shaft of medium steel running on five wood or plastic bushings. The newer set- ups use plastic bushings. The bushings are held in place in the outer tube with ordinary threaded metal screws and the shaft turns inside the bushings. The female threads are in the pipe and the screws protrude into the bushings only a little bit. The bushings should be fitted tightly into the tube housing. It is a very simple set up and the bushings can last years. The galvanized sleeve and inner shaft slides into the hub and is clamped down. The inner shaft slides into a slotted keyway inside the hub. Then there are grease fittings that lube the bearing, cool the unit and help keep water out. There is a steel tail rudder. It helps steer the boat and it curves around and stops just below the prop protecting it from damage. My 13 Hp. engine uses an eight and a half inch two blade prop that is quite weed friendly. Avoid too big of a prop, if you can’t reach the engines top rpm. your prop is too big for that boat and or that engine.

 

THE ENGINE MOUNT CLAMP

 

The engine mount, pivot pin and the mount that is clamped to the boat. Suffice it to say that the clamp must be attached onto the boat as securely as possible and it provides the sleeve bushing that the pivot pin on the engine mount slides into, it resembles a vise. Make it strong as it supports the engine, it doesn’t have to be too heavy duty, unless the engine is say 20 hp. or more.

 

The transoms on many of my boats are slanted at an angle. This is to facilitate having the engine on a transom farther forward and it provides a flotation chamber. A boats bow may rise too much and the boat may become off balance due to too much engine weight aft and there is the pilot’s weight to consider too. Good weight distribution in short long tails are a plus. If you want better performance mount the engine forward. This is not necessarily a hard thing to do. It may be as easy as attaching an engine mount plank 18 inches inboard from the transom.

 

My boats are usually 12 feet long and weigh 50 kilos (130 pounds). If a boat is longer than 12 feet or somewhat bow heavy, mounting the engine a foot or more forward of the transom may not be a necessity. If you already have a boat with a regular transom, it will likely work but it may be good to keep ballast cargo forward. If your boat has an outward angled transom for an outboard set up you will have to weld the motor clamp and pivot pin to a different angle than  on my setup.

 

Asian long tails don’t plane, however my long tails do. The Asian boats are long, very heavy and canoe like. I designed mine for shallow water (2 in. draft), portability and speed. At high speeds my boats are hardly in the water. I have developed a type of boat and application; the long tail hydroplane.

 

My eight foot boat will plane with one person aboard using a 5.5 Hp. engine but the boat, engine and prop are a precisely matched unit. Generally speaking with a long tail set up you won’t get enough power to plane a boat using less than eight horse power. The boat will have to be a good flat bottom performance hull too. Something like a small 50 Kilo. (130 lb.) 12 by 4 foot Garvy. The best engine I have found is a 13 hp. Honda GX 360. I tried a much bigger engine but the weight cancelled out the additional power and the performance was similar to the 13hp engine. The best small boat I make the Nitwing is a true hydroplane. It is five feet wide at the transom and ten feet long, the rear transom is only 8 ½ in high.

 

A very important factor here is the proper size and pitch propeller. Matching the prop to the engine may be hard to get right outside of Asia where the set up is made. I would make friends with the owner of a boat yard and try out his used small outboard engine props to see what works.

ANY QUESTIONS WLL BE ANSWERED

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16 Comments

Reply karel Dawson
4:45 PM on August 17, 2011 
Dear Sir,

I would like to Purchase a complete Diesel engine set with shaft etc for a Long tail boat, can you nplease advise were to purchase.
Reply Nelson Opa
10:10 AM on September 7, 2011 
I want buy one complete long tail with shaft,prop all mounting. Please send cost of 20-30hp diesel
Reply sean
3:39 AM on December 21, 2011 
please use the forum for all questions
A outstanding article,I thinl I will try & build one but do have 3 questions before I start gathering parts.(1) Bearing type, roller ot tapered? If roller what keeps shaft torq from hurting eng brarings?If taper ,how do you adjust preload? (2)Inner shaft coupling to the eng drive, is it a flex,u-joint,orsolid type coupler? (3)what type clamp ,clamps the galvanized sleeve to the hub,or does the pipe sleve screw into the hub? These questions are proably very simple for those people who are familer with the set up, The photos of the eng mount helped alot.Once I start I might have more questions but will try & not trouble you alot. thank you for your help in advance.I am intriged your boats can operate in les than 6in of water, if I am sucessful @ building this eng assy might try a big project of ypur style boat, I love to hunt duck!
[/sulferburner]
Reply sean
3:40 AM on December 21, 2011 
sean says...
please use the forum for all questions
A outstanding article,I thinl I will try & build one but do have 3 questions before I start gathering parts.(1) Bearing type, roller ot tapered? If roller what keeps shaft torq from hurting eng brarings?If taper ,how do you adjust preload? (2)Inner shaft coupling to the eng drive, is it a flex,u-joint,orsolid type coupler? (3)what type clamp ,clamps the galvanized sleeve to the hub,or does the pipe sleve screw into the hub? These questions are proably very simple for those people who are familer with the set up, The photos of the eng mount helped alot.Once I start I might have more questions but will try & not trouble you alot. thank you for your help in advance.I am intriged your boats can operate in les than 6in of water, if I am sucessful @ building this eng assy might try a big project of ypur style boat, I love to hunt duck!

[/sean]
Reply pngpoly
11:27 PM on January 19, 2012 
Hi Sean, I am just curios if you have replied to the the post below with regards to a thrust bearing. I am building a boat now and I have the motor (GX160 Honda) plus a prop and adaptor/Hub. I dont have a shaft as I couldnt bring it back with me on the airplane, and I didnt get a look at one while I was shopping. Does the shaft have any tipe of thrust bearing to take the pressure off the motor?

Cheers
Brendan
Reply sean
12:02 AM on January 20, 2012 
pngpoly says...
Hi Sean, I am just curios if you have replied to the the post below with regards to a thrust bearing. I am building a boat now and I have the motor (GX160 Honda) plus a prop and adaptor/Hub. I dont have a shaft as I couldnt bring it back with me on the airplane, and I didnt get a look at one while I was shopping. Does the shaft have any tipe of thrust bearing to take the pressure off the motor?

Cheers
Brendan


please use the forum for all questions but no bearing in the shaft just the in the hub, a roller bearing, no big load as the inner shaft just slides in with a loose keyway. The shaft has four or five sleeves made of plastic or wood.take the hub apart and see the female keyway and make the shaft with a male counterpart.please use the forum for all questions
Sean I will get around to making a vdeo soon about the setup, please be patient I have been boating...Sean
Reply Darrel
5:44 PM on October 27, 2012 
sean says...
please use the forum for all questions
A outstanding article,I thinl I will try & build one but do have 3 questions before I start gathering parts.(1) Bearing type, roller ot tapered? If roller what keeps shaft torq from hurting eng brarings?If taper ,how do you adjust preload? (2)Inner shaft coupling to the eng drive, is it a flex,u-joint,orsolid type coupler? (3)what type clamp ,clamps the galvanized sleeve to the hub,or does the pipe sleve screw into the hub? These questions are proably very simple for those people who are familer with the set up, The photos of the eng mount helped alot.Once I start I might have more questions but will try & not trouble you alot. thank you for your help in advance.I am intriged your boats can operate in les than 6in of water, if I am sucessful @ building this eng assy might try a big project of ypur style boat, I love to hunt duck!

[/sean]
Reply Jerry Jaksha
10:18 PM on November 10, 2012 
Hi
Thanks for the info.
I am planning to use a setup like this on my nacra 5.0 catamaran sailboat to get out of the marina.
My thought is to use a longtail shaft powered with 3/4 hp electric motor. I will hang it below the cross beams with the motor below the front beam.

Your description of the shafts construction is very helpful.

Jerry
Reply Tjaart
3:38 AM on June 10, 2013 
Hi, I want to know if there is any other uses for the long tail shaft other than using it on the water.
Reply Carl
3:36 PM on August 7, 2013 
I have a 35 foot fishing boat which slow steaming from one place to another. I have seen in movies and on TV large boats using long tails. I was wondering if a long tail coild help increase speed of my boat by a few MPH. Is there a set up for large boats and what size engine would have to be used.

Thanks

Carl
Reply sean walker
11:29 PM on August 9, 2013 
karel Dawson says...
Dear Sir,

I would like to Purchase a complete Diesel engine set with shaft etc for a Long tail boat, can you nplease advise were to purchase.


Like I say everywhere on this site all questions will be answered on the forum onlt and as soon as posssible, Thai Sean
Reply Carl pear
10:59 AM on August 19, 2013 
I have a factory 24 foot bayliner. I'm sure you know the type.
I would like to equip it with a long tail.
Is this possible?
I see some large boats on the net and in films powered this way.It appears to me the hp of a longtail engine is less then say a factory boat like mine. There is a 350 cu. in. in my boat.
High speed is not an necessity. Would, lets say a 4 cylinder, 80 HP diesel engine be suffice. It seems more speed is generated because of the absence of a marine trans mission. Am I correct in this idea?
Any info u can supply would be appreciated.
Thanks
Carl
Reply Lee
4:31 PM on October 17, 2013 
Do you have any pictures? One would be worth a thousand words.
Reply pol
11:59 PM on February 6, 2014 
Hi, I really like your site...I'm renovating a 5m longtail and am struggling for a light but strong engine mount...I have a lightweight engine for the boat....I've screwed in a hardwood bar about 1.5 ft in from the transom for the engine..it's pretty solid however I'm concerned that it will twist eventually under power..do you have any suggestions...I'm wary of adding too much weight aft from additional wood bracing.

regards pol
Reply sean
3:40 AM on February 7, 2014 
pol says...
Hi, I really like your site...I'm renovating a 5m longtail and am struggling for a light but strong engine mount...I have a lightweight engine for the boat....I've screwed in a hardwood bar about 1.5 ft in from the transom for the engine..it's pretty solid however I'm concerned that it will twist eventually under power..do you have any suggestions...I'm wary of adding too much weight aft from additional wood bracing.

regards pol

Use 1/4 in. Aluminum for the mount
Reply Robert
9:03 AM on July 30, 2014 
Please keep me informed about longtailboats and a posible catamaran.

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