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Topic: 21ft Butt cat rebuild  (Read 8424 times)

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Offline John F

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Re: 21ft Butt cat rebuild
« Reply #40 on: July 01, 2017, 05:10:45 pm »
Awesome! Turned out great and super catches too!!!

Well done!  (clap)

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Offline victorius

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Re: 21ft Butt cat rebuild
« Reply #41 on: July 02, 2017, 09:41:36 am »
Congrats great build and great catches

Offline sardinella

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Re: 21ft Butt cat rebuild
« Reply #42 on: July 02, 2017, 11:37:16 am »
Job very well done

Offline shu vawda

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Re: 21ft Butt cat rebuild
« Reply #43 on: July 06, 2017, 01:40:52 pm »
Thank you all.Hopefully i will be posting a new rebuild soon..... w;k

Offline dugong

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Re: 21ft Butt cat rebuild
« Reply #44 on: July 06, 2017, 01:56:33 pm »
Nice!!! :rck" (clap)
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Offline DROM MP

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Re: 21ft Butt cat rebuild
« Reply #45 on: July 06, 2017, 02:14:38 pm »
 :envy

Offline shu vawda

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Re: 21ft Butt cat rebuild
« Reply #46 on: July 18, 2018, 10:39:17 am »
Thank you all.Hopefully i will be posting a new rebuild soon..... w;k


Good Morning everyone.


So as promised, we are starting a new build.this time a bit bigger than the last.Took over my good friends boat who had passed on last year.Its a 27ft butt cat that we will be stripping to the core and rebuilding.


the boat was moored so had to get it out the water this weekend that passed.Took it to natal power boats.They removed the current motors as we will be trading in the old ones for new.


A few questions for the experts out there:


- I am considering installting hull extensions.Is it a good idea?I am looking for extra deck space as we intend installing a new forward console sportfisher cabin
- Would also like a toilet installed.Any brands recommended?Would like one with a motorised flush.
- At the moment io traded the old motors for new 115 suzuki's.The old motors where 115 mercury.i was told by the boat builder yesterday that the 140 suzuki's weigh less than the 115's.is this true and should i rather go for the 140's?
- With the new sportfisher forward console, would i have to add weight at the back of the boat to counter balance?Not sure how the ride would be.


I like the challenge of project boats so hoping this one works out well.I would really appreciate all the feedback.Will keep this thread running as the build unfolds.Boat is now at the boat builders.stripping to commence.


I have attached some pics of our canvass.

Offline Slim Dusty

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Re: 21ft Butt cat rebuild
« Reply #47 on: September 04, 2018, 08:14:26 pm »
Any updates on the refurb.....

Offline shu vawda

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Re: 21ft Butt cat rebuild
« Reply #48 on: October 10, 2018, 12:10:28 pm »
Slim dusty, Yes.


A few items have been done since i last posted.


- We installed 2 layers of glass to to inside of the hull.
- Bulkheads and stringers installed.
- new transom installed.


i have been debating with the family with regards to bouyancy.do we install 2 part pu foam or EVA.I bought some PU and decided to do some tests.The results where shocking.




When PU foam is cut it absorbs alot of water.If poured into a closed compartment it does not fill all the gaps leaving pockets where water could stand although it does have a sealed layer around it which allows for less water to penetrate.With all this said, the PU foam does make the hull most rigid and strong when compared to EVA or bottles.


Due to us now installing a cabin to the front we decided to do the PU foam at the front half and the EVA on the bottom half.Front half would be covered by the cabin so chances of water getting in would be slim.

Offline FishStyx

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Re: 21ft Butt cat rebuild
« Reply #49 on: October 10, 2018, 01:08:51 pm »
Also not a fan of PU foam... After cutting into the foam at the stern of one of my boats to get at engine mount bolts, I realised the stuff is seriously prone to water logging. I still like bottles (the correct ones) but bundled in nets that are fastener to the stringers. Alternatively, SPX foam cut to suit the spaces.
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Offline Visenvryheid

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Re: 21ft Butt cat rebuild
« Reply #50 on: October 10, 2018, 05:29:09 pm »
https://www.sondor.co.za/industries/view/10/marine-floatation

"Sondor manufacture and supply cross-linked closed cell expanded   Polyethylene (SPX) and cross-linked closed cell expanded SVA in various   densities for numerous floatation and buoyancy applications.     Buoyancy Sheeting/ Blocks (SPX) 
  • Sondorís foam is a fully cross-linked closed cell expanded polyethylene.
  • Excellent buoyancy characteristics - able to support approx. 1000 Kg/m3.
  • SPX is fully closed-cell, and will not absorb water even if the material is cut open.
  • Superior tensile strength, elongation and weathering capabilities.
  • Resistant to chemicals, oils, and fuels.
  Sondor SPX complies with SAMSA regulations section 9 &   9.1 regarding floatation requirements. [Category A-E: (Off-shore) as   well as category R: (Inland waters)]"
That is the stuff you want, they float jetties with it..with the blocks of the stuff sitting in the water unprotected for years the jetties are still floating quite fine..

Offline shu vawda

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Re: 21ft Butt cat rebuild
« Reply #51 on: October 10, 2018, 05:30:24 pm »
Fishstyx, how did you manage to rectify this?Once the water is soaked in,there is no way of draining it out so it is normally a task to fix.I hear you on the bottles although this does not improve hull strenght and in my case the older butt cats where manufactured according to being filled with PU foam.I am hoping that the PU foam at the front of the boat provides enough strenght when punching through waves/swells.


The old foam that was taken out was completely waterlogged but when the drain plugs removed, no water came out :dunno:

Offline shu vawda

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Re: 21ft Butt cat rebuild
« Reply #52 on: October 10, 2018, 05:33:48 pm »
https://www.sondor.co.za/industries/view/10/marine-floatation

"Sondor manufacture and supply cross-linked closed cell expanded   Polyethylene (SPX) and cross-linked closed cell expanded SVA in various   densities for numerous floatation and buoyancy applications.     Buoyancy Sheeting/ Blocks (SPX) 
  • Sondorís foam is a fully cross-linked closed cell expanded polyethylene.
  • Excellent buoyancy characteristics - able to support approx. 1000 Kg/m3.
  • SPX is fully closed-cell, and will not absorb water even if the material is cut open.
  • Superior tensile strength, elongation and weathering capabilities.
  • Resistant to chemicals, oils, and fuels.
  Sondor SPX complies with SAMSA regulations section 9 &   9.1 regarding floatation requirements. [Category A-E: (Off-shore) as   well as category R: (Inland waters)]"
That is the stuff you want, they float jetties with it..with the blocks of the stuff sitting in the water unprotected for years the jetties are still floating quite fine..


Thank you brother.It is excellent stuff and i will be using it on the protion of the boat that will be exposed to water.I will be installing a sump as well.due to the boat being moored, it will help to drain sponsons out should any water get in.I hope this is sufficient as it could be a costly exercise to rectify.

Offline FishStyx

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Re: 21ft Butt cat rebuild
« Reply #53 on: October 11, 2018, 07:16:22 am »
Fishstyx, how did you manage to rectify this?Once the water is soaked in,there is no way of draining it out so it is normally a task to fix.I hear you on the bottles although this does not improve hull strenght and in my case the older butt cats where manufactured according to being filled with PU foam.I am hoping that the PU foam at the front of the boat provides enough strenght when punching through waves/swells.


The old foam that was taken out was completely waterlogged but when the drain plugs removed, no water came out :dunno:


I didn't bud... I left it as is. It would have meant complete removal of the deck, removal of the foam and replacement with something else.


I'm of the opinion that a boat should rely on design (shape), hull, deck, bulkheads and stringers ONLY for strength. To expect foam to be a significant contributor to the strength of the vessel is a gamble. If I were in doubt about hull strength then I'd add bulkheads and stringers.
Forgive me Father for I have spinned... It's been three weeks since my last cob session.

Offline L Hooker

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Re: 21ft Butt cat rebuild
« Reply #54 on: October 11, 2018, 07:54:40 am »
I personally would go for Sondor foam if i ever had to redo buoyancy! It can be packed very tight which i suppose would help somewhat with rigidity. Like Fishstyx said id rather improve rigidity by way of additional stringers etc. With most boat builders (i say most not all), i believe they follow correct procedures in sealing their hulls when using foam. I believe a lot  of the water ingress problem comes in with installation of external items often by the new boat owner without sealing off drill holes etc, ie drilling 2 x new holes in transom to fit transducer and not sealing holes correctly with a sealant like sika etc, having boat motors fitted by company XYZ and once again not sealing off correctly. Good luck with the build  (clap)

Offline shu vawda

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Re: 21ft Butt cat rebuild
« Reply #55 on: October 16, 2018, 08:21:50 am »
I personally would go for Sondor foam if i ever had to redo buoyancy! It can be packed very tight which i suppose would help somewhat with rigidity. Like Fishstyx said id rather improve rigidity by way of additional stringers etc. With most boat builders (i say most not all), i believe they follow correct procedures in sealing their hulls when using foam. I believe a lot  of the water ingress problem comes in with installation of external items often by the new boat owner without sealing off drill holes etc, ie drilling 2 x new holes in transom to fit transducer and not sealing holes correctly with a sealant like sika etc, having boat motors fitted by company XYZ and once again not sealing off correctly. Good luck with the build  (clap)


Thanks bud for all the advice.Due to the boat being moored, i have designed it such that we do not have mant holes drilled through the hull.Transducer will be in hull.we installing hull extensions for the motors etc so we should be well covered.I am definately using sondor in the back portion of the boat but will still use the pu in the front covered area.We are installing bulkheads and stringers but you would not believe how much better the ride is with the PU foam.We did it on our last build and the boat ferformed beautifully as compared to prior rebuild when bottles where in place.


will update with more picture during the course of the week.

Offline GT Mayhem

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Re: 21ft Butt cat rebuild
« Reply #56 on: October 16, 2018, 09:30:04 pm »
Hi Shu. You are correct in the pu foam theory. The concept with which the old butt cats were built was based on using minimal glass in the hull and drawing strength from the rigidity of the foam filling every inch of the hull, thus creating a single solid unit just like a surf board and keeping the vessel extremely light for its size.
By adding extra stringers bulkheads etc, what you do is defeat the purpose of the type of hull it was intended to be and may not perform as brilliantly as those old butts performed.
It was not uncommon to see 21ft butt cats with 60's or even 40's for this reason.
As far as longevity goes, they seemed to do just fine.
Kaapies swear by them and their side of the ocean is not something to mess around with.