Rigidity/strength of Tiki 21 deck?

[Bo]

Hi, I just bought a four-year-old Tiki 21 and am concerned about the strength of the three sections that make up the deck. I am a 200lb guy and hear a lot of creaking and a little cracking as I move around. Should I expect this? The decks are built according to plan - so is that normal? Thanks!

[Ian Bamsey]

When I bought my Tiki 21 the decks were as per the plans. They were in a bad way. In particular, I think some of the ply had been damaged by water and frost. In places it was almost biscuit like and I broke some ply around the engine well. Otherwise despite being over 30 years old it stood up to me and the family.

I have now totally rebuilt the decks, although I moved a bit from the original design. My central platform has a deeper engine well and therefore the vertical webs that make it stiff are a little deeper. My side platforms have two length-ways stringers instead of one. Overall I think my design is slightly stronger.

When launching this season, I fell hard on the deck carrying a 28Kg engine. My friend was standing on deck at the same time. It turns out we did actually crack one of the central platform webs which I've now repaired. I only noticed this after a several weeks sailing with two adults. The deck was a bit soft, then I finally found the crack. At no point did it look like the whole thing might fail.

In summary, I'm guessing that if the boat is only 4 years old and well built to plan, you won't have a problem. The decks are a little springy, but that's normal. If it's been in the water for any time, a visual check underneath for any cracks or bonding failures will show up any problems as mold etc. gets in and can be seen as dark lines. If you do get a problem, I doubt it will fail catastrophically. 

I hope that's useful.

Ian

[Bo]

Ian, thanks for your helpful reply! As is, my deck would never stand up to two adults with one falling (I hope you are OK). I have found some water problems so a rebuild or partial rebuild is in order. It sounds like I can rebuild to plans and expect sufficient strength.

Ian Bamsey said:

When I bought my Tiki 21 the decks were as per the plans. They were in a bad way. In particular, I think some of the ply had been damaged by water and frost. In places it was almost biscuit like and I broke some ply around the engine well. Otherwise despite being over 30 years old it stood up to me and the family.

I have now totally rebuilt the decks, although I moved a bit from the original design. My central platform has a deeper engine well and therefore the vertical webs that make it stiff are a little deeper. My side platforms have two length-ways stringers instead of one. Overall I think my design is slightly stronger.

When launching this season, I fell hard on the deck carrying a 28Kg engine. My friend was standing on deck at the same time. It turns out we did actually crack one of the central platform webs which I've now repaired. I only noticed this after a several weeks sailing with two adults. The deck was a bit soft, then I finally found the crack. At no point did it look like the whole thing might fail.

In summary, I'm guessing that if the boat is only 4 years old and well built to plan, you won't have a problem. The decks are a little springy, but that's normal. If it's been in the water for any time, a visual check underneath for any cracks or bonding failures will show up any problems as mold etc. gets in and can be seen as dark lines. If you do get a problem, I doubt it will fail catastrophically. 

I hope that's useful.

Ian

[Brad Ingram]

Hey Bo, 

I built a cedar slatted deck for Beto. I've had six adults sitting on it in pretty good waves with no issues at all. It feels really strong. The only downside to the slats is that you'd have to redesign a motor mount as Beto has no engine. I'm probably going to just build a sled that can be mounted on the rear beam if I get a motor in the future. I have some pictures on my profile. 

Brad

[Bo]

Brad, before I asked my question, I dug around on this site and actually saw your cedar deck and really liked the idea! I thought of building a narrower center pod just for the motor mount (topped with cedar) and filling in the sides with cedar. How's the wetness on yours? Thanks for the reply!

Brad Ingram said:

Hey Bo, 

I built a cedar slatted deck for Beto. I've had six adults sitting on it in pretty good waves with no issues at all. It feels really strong. The only downside to the slats is that you'd have to redesign a motor mount as Beto has no engine. I'm probably going to just build a sled that can be mounted on the rear beam if I get a motor in the future. I have some pictures on my profile. 

Brad

[Ian Bamsey]

The cedar decks look really nice and they will be quite solid. If you plan a sled on the back beam for an engine I you might need to consider the prop position. With a 20'' long shaft motor in the normal place, the prop is only just low enough in the water but often cavitates. If you move to the front of the boat the prop is almost out of the water. The situation is improved with an extra long shaft (Tohatsu make a 25'' I think) or build a lower transom.

The situation will be exaggerated the further back the engine is mounted. Note that when placed this far back, lowering the engine enough runs the risk that the prop is almost lower than the hull skegs which provide some guide and protection from motoring in too little water.

[Éric Bouvéron]

That also seems trange to me, the roof part of the deck. While there are three stringer inside the fore and aft deck, plus one outside, plus a curve which make them even stiffer, the plans call for only two stringer under the roof... I am "only" 85 kg, so it should be allright, but I have hesitated to put three.

[Brad Ingram]

Good point, Ian. I am planning to make a sled like the one on the proa "Madness" that connects under the mast beam and can be lowered from the aft beam. The sled on madness is very low profile and high out of the water when raised. It won't put my engine any farther back than a Tiki 26 engine, and the sled will ride on the top of the water keeping the shaft deep in the water. I only plan on 2-3 hp, so it shouldn't be a big deal to set up. I'll also maintain the entire deck space for lounging and sleeping! This is all, of course, if I decide to add an engine. The Race to Alaska guys make me just want to have a pedal drive or some big sculling oars!

Bo, I noticed that most of the spray comes in from the bows, so a solid vs slatted deck I don't think is that much wetter. I have a trampoline that I can put on the deck to keep it a little drier and have a nice space for cooking where my girlfriend won't lose everything though the cracks! One plus of the slats is that no water pools on the platform.

Eric I also notice some spring factor on my decks and plan to eventually add in some super beefy stringers underneath all parts of the deck. 

[Ian Bamsey]

Brad, I can see your approach is right. I think with a light weight engine mounted as you say, it would work. It will take some careful design and would well be a nice design. I have a 5HP engine which is quite heavy. I find I need a bit of power as we moor up in an estuary with some exciting tides. 

Water on my deck is not a problem and does not pool. However, I had to add anti-skid particles as it was slippery with bare feet when it was just glossy paint.

[Bo]

Ian, when you rebuilt your deck did you glass the entire thing? Or did you just tape the long joints after filleting as the instructions indicate?

[Ian Bamsey]

I taped the major seams. The ply was epoxy coated all over then painted on the top surfaces. I pegged some of the 20mm strips to the ply and to the transom. Not for strength, but it makes alignment easy and helps hold joints right when bonding. I didn't have any plans to work from, just the original decks as a pattern.

[Ian Bamsey]

Sorry, yes, glass the seams after filleting.

[David Kamper]

i recently acquired a tiki 21 but the two side deck panels were missing.  I want to know how the two side deck panels attach to the center panel?   the center panel has a triangle edge along both sides ..  appreciate if someone could advise :)