Author Topic: Motherships and Tenders  (Read 10705 times)

Offline dy031101

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Motherships and Tenders
« on: March 08, 2015, 01:22:54 PM »
I recently came across some illustrations on a series of mothership studies (RP1 is probably more familiar with them) and a study summary chart.  See attachment for details.

I have no idea how the design at the bottom row, middle column of the illustration page works.  Does anyone know?

=====================================================================

So I recently am attempting to toying around the idea of a mothership for four Sa'ar 4.5 class FACs.  Shipbucket has a crane ship design that I can mess around with, so I started with a crane ship:



(And yes, those two cranes are indeed the reason why I started that radar installation thread......)

Do you think a crane ship would work?  Or do you think that a flo/flo type ("Heavy Lift Ship" in that Study Summary) or a Dock Ship with open-topped well deck would be better for FACs with such a tall mast?  :D

Comments and suggestions will be appreciated.
« Last Edit: March 30, 2015, 05:13:46 AM by dy031101 »
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Offline Jeffry Fontaine

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Re: Motherships for small FACs
« Reply #1 on: March 09, 2015, 02:11:43 AM »
Keep it simple.  Lifting things requires certification of the cranes for the weights to be handled.  Swinging a large bulky object off of and on to a ship at sea is going to be an exciting series of maneuvers.  The float on/float off concept makes more sense if the masts can be folded over on the small craft for clearance in the well deck and the Sa'ar class are rather narrow of beam so packing them in two by two on a larger hull should be no problem at all. 

Also consider the stresses of all that weight on the deck while carrying your FAC's.  Weight that is high out of the water and challenging your center of balance.  At least with a well deck the load is lower and closer to the water allowing you to float it in or out without worrying about your cranes going out of service. 

A large LSD type would be ideal for a mother ship.  Base it on a modified container ship or one of those LASH type (Lighters Aboard SHip) cargo carriers with a drop down rear door to allow your FACs to enter or exit the ship. 
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Re: Motherships for small FACs
« Reply #2 on: March 09, 2015, 02:19:42 AM »
No reason why a crane ship wouldn't work (see below), though it does mean more above deck area unable to be used - though on the other hand flo/flo also has issues.





BTW, if you click on the last image, you will see a model build of such.
« Last Edit: March 09, 2015, 02:21:41 AM by GTX_Admin »
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Offline Jeffry Fontaine

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Re: Motherships for small FACs
« Reply #3 on: March 09, 2015, 02:24:52 AM »
Sa'ar Class FAC weighs in at somewhere around 415 tons and swinging that on the end of a crane would be rather exciting. 
"Every day we hear about new studies 'revealing' what should have been obvious to sentient beings for generations; 'Research shows wolverines don't like to be teased" -- Jonah Goldberg

Offline elmayerle

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Re: Motherships for small FACs
« Reply #4 on: March 09, 2015, 02:28:04 AM »
Sa'ar Class FAC weighs in at somewhere around 415 tons and swinging that on the end of a crane would be rather exciting.
Definitely  makes flo-flo look more attractive.  IIRC, there was a technothriller that came out during the 1980's that had the Soviets using a Udaloy (sp?) as a mother ship for a bunch of FAC (ISTR that they were air-cushioned ones, too).

Offline dy031101

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Re: Motherships for small FACs
« Reply #5 on: March 09, 2015, 04:24:08 AM »
Thanks for all the inputs.  :)

The float on/float off concept makes more sense if the masts can be folded over on the small craft for clearance in the well deck......

Not sure- I'm working under the assumption that I'll have to settle with an open-topped well deck for accommodating the Hetz-type vessels......

A large LSD type would be ideal for a mother ship.
Definitely  makes flo-flo look more attractive.

Are there specific advantages and disadvantages for dock ship type (à la LSD) over heavy lift type (à la Blue Marlin) and vice-versa beyond details regarding the entry and exit of "daughter" boats?

Thanks again.
« Last Edit: March 09, 2015, 07:55:47 AM by dy031101 »
Forget about his bow and arrows- why wait until that sparrow has done his deed when I can just bury him right now 'cause I'm sick and tired of hearing why he wants to have his way with the cock robin!?

Offline RP1

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Re: Motherships for small FACs
« Reply #6 on: March 09, 2015, 08:02:16 AM »
Hi,

The middle-lower study is a stern gantry ship. It's basically a LASH barge carrier with funny proportions due to the size and shape of the daughter craft carried.

RP1

Offline dy031101

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Re: Motherships for small FACs
« Reply #7 on: March 09, 2015, 08:21:34 AM »
                   UPC Per Asset
StudyRelative UPCMediumRelativeSmallRelative
Dock1.0041.061.0
Heavy Lift1.1341.1361.13
Crane0.9121.8241.36
Fast Crane1.7223.4342.58
Gantry0.90--41.35
Deep Draught0.97--41.45
SSK Dock0.7412.97--

(Looks like Dock Ship is the cheapest option...... not to mention it saves me the trouble of having to have forward and aft radar masts......)

Would a Sa'ar 4.5 class boat be considered a medium asset or a small one?

Also, what's the difference between "Command" and "Support" variants of the Dock Ship?  For example, does the "Support" variant have better maintenance facility for the boats (or does the "Command" variant not have it)?
« Last Edit: March 09, 2015, 12:59:41 PM by dy031101 »
Forget about his bow and arrows- why wait until that sparrow has done his deed when I can just bury him right now 'cause I'm sick and tired of hearing why he wants to have his way with the cock robin!?

Offline RP1

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Re: Motherships for small FACs
« Reply #8 on: March 09, 2015, 03:09:01 PM »
Hi,

The simplicity of the dock ship made it cheap, although the long length of the dock and flared hull made for *very* large tanks to enable the forward part of the dock to be flooded.

We used an open dock as shown in this rendering: http://rp-one.net/hosted/dk_ms.png as a covered dock would need a very high roof to operate in any real sea state. That being said, if you really wanted a roof some movable fibreglas structure might be possible. It would interfere with the flight deck (which was forward of the dock in this case), however.

The "command" variant moves some of the command personnel from the assets to the mothership, so they are more like fighters than FACs. The "support" variant has improved depot facilities for the daughter craft.

From my speaking notes:

"The three notational Surface Combatants are shown here, a small craft of approximately 200 tonnes displacement, a medium vessel of approximately 600 tonnes and a large vessel of approximately 1000 tonnes.  These are broadly equivalent to the Finnish “Hamina” class, Swedish “Visby” class and Israeli “Sa’ar 5” class corvettes.

(The final displacements for the assets were:
Small  = 297 te / 55 m
Medium = 730 te / 66 m
Large = 1207 te / 74 m)"


RP1

Offline dy031101

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Re: Motherships for small FACs
« Reply #9 on: March 17, 2015, 01:32:42 PM »
The simplicity of the dock ship made it cheap, although the long length of the dock and flared hull made for *very* large tanks to enable the forward part of the dock to be flooded.

We used an open dock as shown in this rendering: http://rp-one.net/hosted/dk_ms.png as a covered dock would need a very high roof to operate in any real sea state.


Because I have an awful sense of scale...... could you suggest how high above or down below the waterline the well deck floor would roughly be?

Thanks.
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Offline RP1

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Re: Motherships for small FACs
« Reply #10 on: March 17, 2015, 05:46:01 PM »
Hi,

In the dock mothership the well deck was 2m (TWO) above the waterline. We considered having it below the waterline to keep the size down but it requires two sets of stern doors, which is complicated to arrange.

RP1

Edited because 1 unit at 1:2 is 2 units at full scale...

Offline Volkodav

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Re: Motherships for small FACs
« Reply #11 on: March 18, 2015, 10:19:08 PM »
The other option could be a cradle arrangement, i.e. each FAC mounted on its own cradle and moved on rails, they could still be launched over the sides but recovered over the stern.

Offline dy031101

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Semi-submersible Seaplane Tenders?
« Reply #12 on: March 30, 2015, 05:58:31 AM »
Sa'ar Class FAC weighs in at somewhere around 415 tons and swinging that on the end of a crane would be rather exciting. 

This got me thinking of another topic......

There are flying boats nowadays with maximum takeoff weight in that class, too- I suppose I won't be using cranes, either, if I want a tender for such flying boats?  Or would empty or gross weight be closer to be applicable when it comes to being serviced?

(I must have been very tired when I typed that.)

If I can't use cranes, The first thing that comes to my mind is a semi-submersible like Blue Marlin...... but Blue Marlin's size seems too big to me, and I haven't seen any smaller semi-submersible.  Has there been a smaller ship of Blue Marlin's configuration?  With something like a 70-metre well deck?

Thanks in advance.
« Last Edit: November 28, 2017, 03:57:55 PM by dy031101 »
Forget about his bow and arrows- why wait until that sparrow has done his deed when I can just bury him right now 'cause I'm sick and tired of hearing why he wants to have his way with the cock robin!?

Offline Volkodav

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Re: Motherships and Tenders
« Reply #13 on: March 31, 2015, 08:53:34 PM »
The other option is a Mobile Landing Platform (MLP)

http://en.wikipedia.org/wiki/Mobile_Landing_Platform

They are designed to transfer stores and equipment from HSVs and more conventional transports to LCACs and helicopters.  A version designed to carry four to six FAC or even corvettes could be developed.  As they are based on tankers the bunkers could be converted to ballast tanks to maintain stability when launching and recovering vessels.  A side launched cradle would be the way to go over cranes, sliding down an angled section of deck until the launched vessels floats off and just repeat for recovery, in an emergency they could be manually slid down into the water and motor away.  Alternatively the entire mother ship could just immerse its self and float the vessels of rigid cradles on the deck.

Offline RP1

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Re: Motherships and Tenders
« Reply #14 on: April 01, 2015, 12:03:55 AM »
I have a picture somewhere of a tender proposed for the Sea Master jet flying boat which just hauled the aircraft up an artificial beach. If you were willing to design your daughtercraft to be launched a recovered this way then it might be easier than cranes. We needed to be able to handle daughter craft with propellers and normal hullshapes, however, so that wasn't an option in the mothership study.

RNLI lifeboats would provide a model for a daughter craft compatible with an artificial beach - waterjet propulsion, strakes to support the aft end, rubbing strips / rails on the three contact points (centreline keel and side strakes) and a lot of local structural reinforcement. Of course, as you are operating from a mothership, you could trade off some endurance for additional structure.

Handling when pulled up the beach would be by some kind of trolley (a big one!). But this would never go near the water and could perhaps use lots or rubber tyres on a guideway rather than be a true rail system to avoid the usual concerns over rail alignment on ships.

The nice thing about this is that, apart from the round-down for the beach at the stern, the ship would be relatively conventional and most importantly would not need to dock down with the resultant survivability issues - those heavy lift ships sink by accident occasionally! That being said, there are some solutions (massive sponsons).

RP1


Offline The Big Gimper

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Re: Motherships and Tenders
« Reply #15 on: April 01, 2015, 12:35:11 AM »
I have a picture somewhere of a tender proposed for the Sea Master jet flying boat which just hauled the aircraft up an artificial beach. If you were willing to design your daughtercraft to be launched a recovered this way then it might be easier than cranes. We needed to be able to handle daughter craft with propellers and normal hullshapes, however, so that wasn't an option in the mothership study.

RNLI lifeboats would provide a model for a daughter craft compatible with an artificial beach - waterjet propulsion, strakes to support the aft end, rubbing strips / rails on the three contact points (centreline keel and side strakes) and a lot of local structural reinforcement. Of course, as you are operating from a mothership, you could trade off some endurance for additional structure.

Handling when pulled up the beach would be by some kind of trolley (a big one!). But this would never go near the water and could perhaps use lots or rubber tyres on a guideway rather than be a true rail system to avoid the usual concerns over rail alignment on ships.

The nice thing about this is that, apart from the round-down for the beach at the stern, the ship would be relatively conventional and most importantly would not need to dock down with the resultant survivability issues - those heavy lift ships sink by accident occasionally! That being said, there are some solutions (massive sponsons).

RP1


This one?

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Offline RP1

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Re: Motherships and Tenders
« Reply #16 on: April 01, 2015, 02:04:28 AM »
I'm not sure - I think it was for the nuclear-powered version of the Sea Master.

Offline GTX_Admin

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Re: Motherships and Tenders
« Reply #17 on: April 01, 2015, 02:46:52 AM »
I have a picture somewhere of a tender proposed for the Sea Master jet flying boat which just hauled the aircraft up an artificial beach.


This one I presume:

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Re: Motherships and Tenders
« Reply #18 on: April 01, 2015, 02:49:04 AM »
Speaking of which...

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Offline dy031101

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Aerostat Tender
« Reply #19 on: April 07, 2015, 10:40:45 AM »
I have a picture somewhere of a tender proposed for the Sea Master jet flying boat which just hauled the aircraft up an artificial beach. If you were willing to design your daughtercraft to be launched a recovered this way then it might be easier than cranes.

If what I'm looking for this time around is just a tender for amphibious aircraft, would I still be needing that trolley?

===============================================================

Well well well...... an inspiration when I wasn't going out of my way to look for it:
« Last Edit: April 07, 2015, 01:07:06 PM by dy031101 »
Forget about his bow and arrows- why wait until that sparrow has done his deed when I can just bury him right now 'cause I'm sick and tired of hearing why he wants to have his way with the cock robin!?

Offline RP1

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Re: Motherships and Tenders
« Reply #20 on: April 07, 2015, 02:26:04 PM »
I think the need for the trolley would be dictated by the design of the airplane and whether it needed beaching gear or not.

I wondered when someone would find the aerostat tender (not mine - one of our PhD students, now a post-doc; https://www.ucl.ac.uk/mecheng/people/researchers/dr-nick-bradbeer)  :)

RP1

Offline dy031101

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Seaplane Tender Question
« Reply #21 on: April 26, 2015, 02:02:52 PM »
I've been reading up on seaplane tenders lately and found a paragraph here a bit puzzling.

Quote
The extra space on the aft-deck allowed the crew of the air maintenance division added working room in which they could operate without interference from the hanger area.


I've been under the impression that hangar is working deck with protection from weather.  What, beyond hoisting seaplanes from and down to surrounding water, is the aft-deck on Curtiss and Currituck classes meant for that can be interfered from the hangar?

=========================================================================

Also, a lot of mentions of Currituck class tenders that I came across make reference on a catapult supposedly meant for the abortive floatplane version of the Helldiver dive bombers, but I can't seem to find any pictures of any Currituck class vessel with the catapult.  Does anyone know where exactly on the ship's aft is the catapult supposed to be?

Thanks in advance.
« Last Edit: April 26, 2015, 02:14:24 PM by dy031101 »
Forget about his bow and arrows- why wait until that sparrow has done his deed when I can just bury him right now 'cause I'm sick and tired of hearing why he wants to have his way with the cock robin!?