Cruisers Forum
 


View Poll Results: Aesthetics of the PROPORTIONS of the long prop drive system? (instead of out/inboard)
Love it! 5 29.41%
Hate it! 4 23.53%
Indifferent - you do you man. 6 35.29%
Acquired taste - perhaps I could get to like it? 2 11.76%
Voters: 17. You may not vote on this poll

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 13-01-2023, 11:24   #1
Registered User

Join Date: May 2016
Boat: slowly designing a worldcruiser for early retirement
Posts: 37
Thailand longtail type propulsion pro/con?

What do people here think about the type of propulsion used on thai longtail boats? It's used elsewhere in southeast asia too but seems to have a really strong following in thailand.




Personally I like them alot and I see many practical advantages. The aesthetics could be hit or miss/whether someone minds being different, but since it looks different i'm used to people probably thinking they'd rather not have one even if it saved tens of thousands of dollars. What would you think if something with a motor like that pulled next to you in the marina?



I'm not saying that it has to look JUST like this with the engine's naked rumpus hanging out in the wind, a person could make fiberglass or metal cowls or coverings just like outboards have, it could look downright swoopy, but this design would still have the proportions of the long prop shaft. I'm willing to overlook aesthetics to have performance, cost savings, and practical advantages though. First I just wondered what the general consensus was.
black_sails is offline   Reply With Quote
Old 13-01-2023, 11:32   #2
Registered User

Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,207
Re: Thailand longtail type propulsion pro/con?

There are advantages for certain scenarios such as running in very shallow water or wanting to easily adapt any available engine to marine use as an outboard. But the added length has practicality issues, especially for close quarters maneuvering (where outboards are often turned to a significant angle). Some of the low budget, home built ones may forgo having reverse or any kind of reduction gearing as well.



As a result, they're common in some areas (and commercial versions of them are available, at least in small sizes), but the more conventional outboard form factor has remained common in most places.
rslifkin is online now   Reply With Quote
Old 13-01-2023, 11:52   #3
Registered User

Join Date: Jan 2023
Posts: 1,422
Re: Thailand longtail type propulsion pro/con?

Quote:
Originally Posted by black_sails View Post
What do people here think about the type of propulsion used on thai longtail boats? It's used elsewhere in southeast asia too but seems to have a really strong following in thailand.




Personally I like them alot and I see many practical advantages. The aesthetics could be hit or miss/whether someone minds being different, but since it looks different i'm used to people probably thinking they'd rather not have one even if it saved tens of thousands of dollars. What would you think if something with a motor like that pulled next to you in the marina?



I'm not saying that it has to look JUST like this with the engine's naked rumpus hanging out in the wind, a person could make fiberglass or metal cowls or coverings just like outboards have, it could look downright swoopy, but this design would still have the proportions of the long prop shaft. I'm willing to overlook aesthetics to have performance, cost savings, and practical advantages though. First I just wondered what the general consensus was.
If you really like them, I am guessing nothing we can say will change your mind, but a couple things to think about.

If you are pulling into a marina slip, they are going to charge you for all that extra length hanging off the back of your boat. I am guessing increasing the length of your boat by 20%? That's going to add up to a lot of money over a relatively short period of time, but something you might be willing to pay for.

Or, if you are using a longtail as power on a larger boat's tender, you are going to be a VERY unpopular guy at the dinghy dock with that prop hanging out there...

Depending on the kind of boating you do, it might be a challenge handling one of these in close quarters. The damage you could inflict on your neighbors might be horrifying.

Otherwise, it's just another way to make a boat go. None are perfect, all are compromises.
SailingHarmonie is offline   Reply With Quote
Old 13-01-2023, 12:15   #4
Registered User

Join Date: May 2016
Boat: slowly designing a worldcruiser for early retirement
Posts: 37
Re: Thailand longtail type propulsion pro/con?

Quote:
Originally Posted by SailingHarmonie View Post
If you really like them, I am guessing nothing we can say will change your mind,


If you are pulling into a marina slip, they are going to charge you for all that extra length hanging off the back of your boat.

Or, if you are using a longtail as power on a larger boat's tender, you are going to be a VERY unpopular guy at the dinghy dock with that prop hanging out there...

Depending on the kind of boating you do, it might be a challenge handling one of these in close quarters.

I'll put you down as 'not a fan' then.


Some of the longtails can have the prop swing around 360 degrees, you can basically bring the prop right up onto the deck of the boat to defoul it or something.


I'm also not necessarily meaning this would be the ONLY method of moving the boat - a small maybe even electric outboard could work for maneuvering and close in - i'm far more considering these for where room and space is not an issue like in a large lake or the ocean. Where the outboards of equivalent power cost 10x as much. I'm wondering if there's downsides I don't know about in that use practically, or if it's more "people just think its ugly" which is often a way of saying unfamiliar.
black_sails is offline   Reply With Quote
Old 13-01-2023, 12:16   #5
Registered User
 
Shrew's Avatar

Join Date: Aug 2010
Posts: 3,087
Re: Thailand longtail type propulsion pro/con?

What problem are you having that these solves for you? Just getting it for the sake of getting it makes no sense. They make beaver tail/gator tail outboards which serve the same purpose with a significantly better design. JMHO
Shrew is online now   Reply With Quote
Old 13-01-2023, 12:54   #6
Registered User

Join Date: Mar 2007
Location: Santa Cruz
Boat: SAnta Cruz 27
Posts: 6,711
Re: Thailand longtail type propulsion pro/con?

Nobody has mentioned that the average longtail has straight pipe exhaust system. Maybe its for safety as you can hear them a mile away.
donradcliffe is offline   Reply With Quote
Old 13-01-2023, 13:08   #7
Marine Service Provider

Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 6,275
Re: Thailand longtail type propulsion pro/con?

I have a friend that goes duck hunting and has a craft very similar to the "longtail", a common type duck hunting vessel I've been led to understand

The engine is a Briggs and Stratton air cooled engine, it's direct drive only...no reverse...he sez he can travel in 6" of water...the boat itself is a flat bottomed aluminum skiff type craft...not sure how much hp....20 maybe...

might be good for duck hunting...but as a boat's tender...leaves a lot to be desired...
MicHughV is online now   Reply With Quote
Old 13-01-2023, 15:50   #8
Registered User

Join Date: May 2016
Boat: slowly designing a worldcruiser for early retirement
Posts: 37
Re: Thailand longtail type propulsion pro/con?

Quote:
Originally Posted by Shrew View Post
What problem are you having that these solves for you? Just getting it for the sake of getting it makes no sense. They make beaver tail/gator tail outboards which serve the same purpose with a significantly better design. JMHO

Money and performance mostly. 250-300hp is not a cheap outboard. I get that from a Chevy LS from the junkyard for under $500. I don't even need that much power, I just mean a 4cyl isn't much cheaper and a 120hp outboard is still pricey.



There ARE other advantages, significant ones. They like them in shallow waters because you can control the depth of the prop very easily. If you're about to go over weeds you can just lift the prop over as you skate through instead of fouling it up. If youre going over a sandbar, you can literally do a zero depth slide with some momentum and not break and damage your outboard whether you lift the prop out of the water to be safe or not. If you were to go over a log and you don't catch it in time, there's something about the real long lever arm that it just kind of bounces up not too violently or uncontrollably fast and instead of tearing the prop out of the end the blades just bounce the light end off the object. With the weight on the engine side and the end of the prop as light as possible it skips up when hitting an object very very easily.


I read some article once about increased efficiency but I don't remember the exact terms or idea, something about being able to be both fully submerged and semi cavitating at higher speeds means you cover from say 5-35 knots with total efficiency. I'm pretty sure i've read a prop optimized for 35 knots wont trawl as efficiently at 7 knots, but apparently a longtail prop drive can. They can go quite a bit faster than 35 knots too but I don't know if efficiency drops off. This is entirely due to controlling the submersion depth of the prop instead of being a fixed depth like an out/inboard.
black_sails is offline   Reply With Quote
Old 13-01-2023, 16:14   #9
Registered User

Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,207
Re: Thailand longtail type propulsion pro/con?

I foresee some issues in rough water though. Once the boat is pitching, you'll need a lot of angle change to keep the prop in the water. And when you angle down that much, your shaft angle will be significant, sacrificing a lot of efficiency.

For the depth control, there are hydraulic jack plates available that can move an outboard up and down as desired (in addition to existing trim adjustment).

Any prop drive is going to be optimized for one speed range and sacrifice some efficiency in other ranges. There's nothing inherent to a long tail that should mitigate this more than you could with any other setup.
rslifkin is online now   Reply With Quote
Old 13-01-2023, 16:33   #10
Marine Service Provider

Join Date: Jan 2019
Boat: Beneteau 432, C&C Landfall 42, Roberts Offshore 38
Posts: 6,275
Re: Thailand longtail type propulsion pro/con?

let's cut to the chase here......
a "longtail" setup is TOTALLY unsuitable to act as a boat's tender from a dozen different perspectives...so get real..and fugetaboutit....
MicHughV is online now   Reply With Quote
Old 13-01-2023, 17:12   #11
Registered User
 
Alan Mighty's Avatar

Join Date: Mar 2014
Location: Moreton Bay
Boat: US$4,550 of lead under a GRP hull with cutter rig
Posts: 2,135
Re: Thailand longtail type propulsion pro/con?

Quote:
Originally Posted by black_sails View Post
I read some article once about increased efficiency but I don't remember the exact terms or idea, something about being able to be both fully submerged and semi cavitating at higher speeds means you cover from say 5-35 knots with total efficiency. I'm pretty sure i've read a prop optimized for 35 knots wont trawl as efficiently at 7 knots, but apparently a longtail prop drive can. They can go quite a bit faster than 35 knots too but I don't know if efficiency drops off. This is entirely due to controlling the submersion depth of the prop instead of being a fixed depth like an out/inboard.
Sounds in part like the not-fully realised dreams of:

* the Hickman Sea Sled (see https://en.wikipedia.org/wiki/Hickman_sea_sled);

- which evolved into Hickman Sea Sled hull plus Hickman surface propeller drive combination that culminated (perhaps?) in the USN's end-of-WW1 successful trial of wooden-hull aircraft carriers powered with a Hickman surface propeller drive (see Dave Gerr's take at: https://www.gerrmarine.com/Articles/SeaSleds.pdf)

* Renato Levi aka Sonny Levi and his delta dart hulls combined with a surface drive (see: https://www.mby.com/news/81009-81009)

- one expression of which was Dick Branson's Virgin Atlantic Challenger II (see https://powerboatmagazine.co.nz/virg...-on-the-water/)

- and from which the German naval architect/cruiser Rudi Scholz (who has posted on CF - but not recently; last I heard Rudi was based in Philippines and/or Deutschland) produced the Levi Diamond Back surface propeller (Diamond Back Propeller | Welcome to the World of the Original Surface Drive | Levi Drives International) and, more generally, a line of Levi Drives (surface propeller + housing and steering) suitable for small runabouts and coastal fishing vessels (see: LD 170 – 150 | Welcome to the World of the Original Surface Drive | Levi Drives International) and upwards.
__________________
“Fools say that you can only gain experience at your own expense, but I have always contrived to gain my experience at the expense of others.” - Otto von Bismarck
Alan Mighty is offline   Reply With Quote
Old 13-01-2023, 17:16   #12
Registered User

Join Date: Feb 2022
Posts: 21
Re: Thailand longtail type propulsion pro/con?

They’re potentially very fast
PSGB is offline   Reply With Quote
Old 13-01-2023, 17:46   #13
Registered User

Join Date: Mar 2009
Location: Southern Chesapeake Bay
Boat: Norseman 430, Jabberwock
Posts: 1,411
Re: Thailand longtail type propulsion pro/con?

Interesting, but if you are thinking about doing this, better make sure the transom is braced for it. All thrust is on the top of the transom, not spread out down lower.

The double ender you pictured is braced naturally.
ggray is offline   Reply With Quote
Old 13-01-2023, 17:51   #14
Senior Cruiser
 
boatman61's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Jan 2010
Location: PORTUGAL
Posts: 30,583
Images: 2
pirate Re: Thailand longtail type propulsion pro/con?

I've always felt these would be great for Wharrams...
__________________

It was a dark and stormy night and the captain of the ship said.. "Hey Jim, spin us a yarn." and the yarn began like this.. "It was a dark and stormy night.."
boatman61 is online now   Reply With Quote
Old 13-01-2023, 18:08   #15
Registered User

Join Date: May 2016
Boat: slowly designing a worldcruiser for early retirement
Posts: 37
Re: Thailand longtail type propulsion pro/con?

Quote:
Originally Posted by rslifkin View Post
I foresee some issues in rough water though. Once the boat is pitching, you'll need a lot of angle change to keep the prop in the water. And when you angle down that much, your shaft angle will be significant, sacrificing a lot of efficiency.

For the depth control, there are hydraulic jack plates available that can move an outboard up and down as desired (in addition to existing trim adjustment).

Any prop drive is going to be optimized for one speed range and sacrifice some efficiency in other ranges. There's nothing inherent to a long tail that should mitigate this more than you could with any other setup.

Thats a good point... For some reason I hadn't thought as much on that aspect, every 'thai fast boat' vid i've seen has been on water smooth as sheets of glass... rougher water at slow speed might matter less. But then you usually arent trying to plane 35 knots in rough water ANYWAY..

There might be a way to do something like a 'trim' tab on an airplane where you have a constant hydraulic pressure to keep it at a given depth when not in the shallow area, but I realize another option is to stick with an outboard or inboard. With as long as the shaft is, the angle of the prop is not radically different, i'm not sure what the efficiency loss would be but probably not so bad IF the purpose of the boat is fun or getting to fishing spots fast and you're not out in rough weather except to get back home when the clouds are rolling in. This is my expected use in MN anyway even if i'm curious how it'd handle along the ocean coastline.



The specific boat I was planning to use one for was going to be in minnesota so far, but some of our larger lakes when things get windy might challenge. I was not sure which lake i'd be using it on. On the calm ones where i'd like to go fast it'd probably still be fun and worth doing so far..


However apparently there IS something in the longtail that mitigates the prop design and it's the ability to operate fully submerged or semi cavitated. I'd have to dig up the article but it's not on this computer. By changing the depth and degree of cavitation (and the expert sailors of these learn to do it by feel, they can just feel how to make it faster/how deep to go) it changes the characteristics of the prop. The fast drag boat props like that run with the prop half in the water I think, but if totally submerged and running slow are still pretty efficient. Not as efficient as a large prop, but more efficient than a high speed only semi cavitating outboard.
black_sails is offline   Reply With Quote
Reply

Tags
propulsion, Thailand

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Swim Platform - Pro & Con vldevin Monohull Sailboats 21 03-09-2018 10:48
Pro's and Con's of storage on the hard Gulfislander Anchoring & Mooring 18 09-10-2012 02:47
Single vs Dual Wheel. Pro vs Con? dgasmd Seamanship & Boat Handling 18 20-06-2012 04:19
Boat Mortgage Pro's & Con's? Deep-sea-Lee Dollars & Cents 4 21-04-2011 08:54
Twin keel v Fin keel, pro's n con's ? Davegw Monohull Sailboats 6 12-02-2009 02:08

Advertise Here


All times are GMT -7. The time now is 08:02.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.