1981 16' Fiberglass Tri Hull

[PilotColt]

I have a 1981 Fiberglass Tri Hull with a 1972 Evinrude 85 HP 2 stroke. The boat has been sitting up untouched for around 5 years. I got the motor running and took the boat out to make sure the motor ran good throughout the whole power range. Now I need to pull the deck up. The deck is extremely soft on at least the back half of the boat and needs replacement. I have done a lot of reading and prepared to replace all the stringers and the deck. I am also planning to do the transom, although it doesn't have any leaks or residue and the transom doesn't flex when jerk on the tail of the motor. Would it be best to cut the floor to look at stringers and deck replacement or go ahead and pull the motor and rub rail to lift the whole cap off for complete access. The deck also has two ridges from the steering wheel going towards the bow from each side in a V shape and I am unsure on how to replicate this on a new deck installation. There is also a crack in the right hand gunnel. The two under deck pictures are taken from the transom looking forward from in front of the battery.

 

[Bondo]

The deck also has two ridges from the steering wheel going towards the bow from each side in a V shape and I am unsure on how to replicate this on a new deck installation.

Ayuh,...... Welcome Aboard,...... Those are the inside of the hull, cut 'em out, 'n you'll be lookin' at the shop's floor,.....

Only the flat part inside is the deck, which is tapered into the inside of the hull,......

 

[sphelps]

Ayuh,...... Welcome Aboard,...... Those are the inside of the hull, cut 'em out, 'n you'll be lookin' at the shop's floor,......

I concur ! :lol:
‘Taking the cap off would be the best option to gain access imho ..

 

[PilotColt]

I am working on removing the rub rail right now to start removing the cap. The rail is riveted on and then there are spaced rivets holding the cap and hull together so easy enough to drill out. I am trying to find the best way to support the hull on the trailer so that it will not warp when removing the floor and stringers. I am thinking of shimming around the current bunk rails with foam board. I do not know what else is needed. I do plan to replace one stringer at a time, as caution to help keep from flexing the hull too much.

 

[sphelps]

Sounds like a plan ... Shoring up with rigid foam should work if you have it around ..

 

[PilotColt]

So far, I have the keel supported in 3 spots and the chines blocked one in the front and one in the rear on both sides (4 total). I pulled the motor and mounted to an engine stand. I have removed the entire rub rail and drilled out all of the rivets. Next up is getting the cap off this coming week/weekend.

 

[PilotColt]

While waiting on some help to get the top off this weekend, I have begun tearing up the floor. There appears to be 3 full length stringers with 2 additional supports running half way under the main floor. The main middle stringer is so rotten there is not even any wood in it and there is foam filled under the floor on both the LH and RH outer sides.

 

[PilotColt]

I am planning to cut out the stringers as close to hull as possible with cutting wheel then use Douglas Fir stringers made from 1x8s, 1x6s, and 1x4s. The main stringer in the middle appears to only have one layer of CSM with the occasional piece of cloth laid over it, but not across the entire length. I am trying to restore the boat to original condition which means similar materials and lay up schedules. I plan to use polyester resin, I know it is not the best but it sufficient and budget friendly. I have at least 2 potential options. Thinking of using either .75 or 1.5 oz CSM with 1700 cloth and another layer of CSM or strictly 2 layers of 1708 biaxial with CSM tabbing.

Any suggestions or additional guidance/ideas greatly appreciated

 

[sphelps]

You would be better off using plywood for your stringers .. use the 1708 to tab into the hull bottom and up the sides . You can also go over the tops or use the 1.5 csm to seal the tops ..

 

[PilotColt]

My stringers are about 3/4" thick (1" with the fiberglass). (1) 1x8x12' (2) 1x6x6' (2) 1x6x12'. I am assuming that if I use 3/4" plywood for the longer pieces I would have to use a scarf joint then say tab in with 2 pieces of 1708 and cover with CSM.

The reason ply wood would be better then say a douglas fir is because of ... alternating layer directions giving more strength??

 

[sphelps]

Yep
You could probably dimensional lumber and be fine .. Most use plywood ..That’s probably what it was originally ..

 

[PilotColt]

The original fiberglass job on this boat looks very poor. The transom has a very thin layer of chop strain and I can see a little bit of woven fiber, but it appears to only cover the bottom half of the transom. The main stringer in the middle appears to only have one layer of CSM with the occasional piece of cloth laid over it, but not across the entire length, and the other stringers all appear to be chop strand only. Everything is paper thin, less than 1/8" (maybe a 16th). I can confirm from whats left of the rotten wood that the transom is 3 layers of 1/2" ply and the stringer are dimensional lumber. I will use 1/2" marine ply for transom and Douglas Fir for stringers. As far as the fiberglass goes is where I have questions.

I am thinking of doing .75 CSM to tab in the do either 1 or 2 layers of 1708 followed by a top full layer of .75 CSM

on the transom a layer of .75 CSM 1708 .75 CSM 1708.

I have no idea of how many yards of 1708 and CSM to get. On the transom 4 yards of 1708 and 4 yards of CSM. On the stringers 5 yards of CSM to tab 10 yards of 1708 (20 yards if doing 2 layers) and 10 yards of CSM to cover. 10 yards CSM for the top of the deck (only going to resin the bottom of deck).

15-25 yrd 1708
30 yrd CSM

polyester resin is 150 oz weight per gallon.
5.25 - 8.5 gallons for 1708
3.2 Gallons for CSM

Total of 10 gallons or 15 gallons (if doing a second layer of 1708 on stringers).

Which layup should be sufficient and are these calculations anywhere close to accurate ??

 

[chevymaher]

Woodenglass has the estimation in the stickies. I on a 17 footer used 22-23 gallons resin. The 1708 I barely used more then he estimated. Now I used CSM up like it was on fire. I also followed his plan on stringers with the exception I did seal eveything with csm (encapsulate as it is called. Before even going in. Explaining my heavy use of that. 2 and sometimes more of 1708 on stringers.

WOG’s Suggested Materials List for Total Restore of a 16-18’ 3 - Stringer Boat.
It's impossible to give an exact "Quote" of everything you'll need but this list will get you "Started" and from there,
after you've done some "Glassin" you should have a good idea of what you'll need to "Finish-UP"
Here's the Starting List.
PPE
Respirator (Full Face Preferred $100) if not then double filtered 1/2 face and Goggles with vents
taped over.
Latex Gloves (1 – 2 Box(s))
Leather Gloves 1 Pair
Full cover Hooded Tyvek suit. (Rubber Band or Tape the Wrists and Ankles, wet Towel around your
neck)
Talcum Powder (coat yourself TOTALLY with talcum powder prior to every grinding Session. USE A
LOT)
Demo Equipment
Prybars, Hammers, chisels, Putty Knives
Flat tipped shovel to remove foam, Old Carpenters Saw (The Old “Fox Hole” Army Surplus Shovels
work well)
Circular Saw
Sawzall
Dremel Tool
Multi Tool
Router
Drill
Random Orbit Sander
Rasps, Files
4 1/2" or 7” Grinder with Backup Pad and 24 grit resin coated sanding discs
Masking Tape
Shop Vac for dust control or Dust Collector if you're fortunate enough to have one. (Get the internal
bags for the Vac)
It's good to create a Plastic Tent over the boat to contain the dust. There WILL be a LOT of it....A
LOT!!!!
Glassing and Wood Products
3-4 sheets 3/4" Arauco Ext. Grade Plywood(Any good quality External Use Plywood will work)
(Possibly some 1⁄2” and 1⁄4” for side panels and seat bases when and where needed”
15 -20 Gallons 435 Polyester Resin Or Epoxy
4 gals Cabosil
1 lbs 1/4" chopped strand fibers (not needed if using epoxy)
5 yds 1.5 oz CSM (not needed if using epoxy)
20 yds 1708 Biaxial Cloth (use 17oz biax fabric if using epoxy)
2 dozen 1 qt plastic mixing buckets and stir sticks
1 - 1/2" x 5" Fiberglass "Bubble" roller
2 dozen Short nap 6" nylon roller covers and trays
2 dozen 3" Chip Brushes (cut 1⁄2 the length of the bristles off)
5 Gallons of Acetone.
Tri-Sodium Phosphate (buy it at Lowe’s)

 

[Scott Danforth]

I am planning to cut out the stringers as close to hull as possible with cutting wheel then use Douglas Fir stringers made from 1x8s, 1x6s, and 1x4s. The main stringer in the middle appears to only have one layer of CSM with the occasional piece of cloth laid over it, but not across the entire length. I am trying to restore the boat to original condition which means similar materials and lay up schedules. I plan to use polyester resin, I know it is not the best but it sufficient and budget friendly. I have at least 2 potential options. Thinking of using either .75 or 1.5 oz CSM with 1700 cloth and another layer of CSM or strictly 2 layers of 1708 biaxial with CSM tabbing.

Any suggestions or additional guidance/ideas greatly appreciated

you should use plywood for stringers. fir would have no strength compared to plywood on end

poly resin is more than enough

and for guidance, read the threads in their entirety that are in links 14, 15, 18, 2, 3, 4a, 4b and then 1

https://forums.iboats.com/forum/boa...r/295740-how-to-s-and-other-great-information

 

[PilotColt]

PROGRESS

I have been very busy and not able to devote more time to this project. Over the last few weeks I have removed everything and down to just needing to complete the final sanding with 40 grit before we can go back together.

The stringers were mushy and completely gone on the top but the bottom 1.5" was solid, dry, and put up a bit of a fight.

 

[buxmj]

Great progress, I am on my 2nd multi tool and hope my next one won't be purchased to work on the boat! I don't think I have seen any good sections of factory glass on any of the threads on this site, amazing how bad the factory quality is. A fiberglass repairman who has given me some advice told me I would be surprised at how much work he does on new boats before they are sold, that is just crazy.