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Old 15 May 2008, 12:20   #1
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Wave riding. Transom damage?

Hi guys,

New owner of the RIB and first time poster here. I have small 3.85m PVC RIB with soft bottom and aluminum floor + 15hp 2str Yamaha outboard (~40kg). Boat is rated for max 25hp motor. Most usage is in inland lakes some of them are big :| with rough water (Lake Simcoe for example). Without wind I could easily get 28km/h speed but when wind gets > 15-20 km/h I am afraid I can snap transom off if I would jump on the waves.

So question is do I need to be afraid or it is not easy to damage transom?

Any thoughts are appreciated.
Thank you,
Dmitry
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Old 15 May 2008, 12:29   #2
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Hello. I don't think you'll damage the transom. However, there is a weak point on some aluminium floored boats - if the floor is sectional and held together by rails along the sides, the front section of floor can fail at the end of the rail if driven hard into waves.
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Old 15 May 2008, 14:32   #3
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Thanks for quick reply.

You think is more likely I will damage sectional aluminum floor than tear off transom from tubes?

Do you know if there is a way to secure panels? However front D panel (1 of 4) not even secured with rails ...
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Old 15 May 2008, 15:04   #4
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On Zodiacs, the aluminium floor is secured with stringers positioned either side which are held in place through the pressure of the sponsons. If the SIB is rated for 25 HP I doubt it very much that you're likely to damage the transom. (See attached). You may hear a few creaks, but this is just the floor flexing.

There are after-market ways to strengthen your transom, such as support brackets which bolt to the floor and transom, or an aluminium runner up both sides of the floor (bolted at intervals) to hold floor rigid. I've seen this on a MK 3 Zodiac in addition to the stringers.
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Old 16 May 2008, 09:25   #5
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Hi Dmitry

I have a 4.3m Yamaha SIB with aluminium floor and 30hp Yamaha 2 stroke on the back (I cannot recall the exact weight of that engine, but it's heavy!). In rough water you do get a lot of noise from the aluminium floor but I have never worried about it or the transom. If your boat is rated up to 25hp I am sure you will be just fine.

I have, however, hit a wave hard a couple of times causing the bow of the boat to 'fold' up where the D floor panel (which is plywood on mine) meets the first aluminium panel. Like your boat, my front panel does not have side rails. This seems the weak point similar SIBs I have looked at and, to avoid problems, I tend to slow down when it gets rough. Suggest you do the same!
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Old 16 May 2008, 10:11   #6
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Thanks for the answers, guys!

I'm not abusing my SIB but sometimes you can get there on a still water and get back on rough. Min planing speed for the boat and motor 20km/h (gps) with 2 adults. It is still fast for some waves.

I'll probably think of some floor frame for particular lakes. Glad I do not have to worry about transom.

PS Boat specs initially allowed 30hp but specs were lowered due to 4 strokes I believe.
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Old 16 May 2008, 11:57   #7
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Originally Posted by dim. View Post
Hi guys,

New owner of the RIB and first time poster here. I have small 3.85m PVC RIB with soft bottom and aluminum floor + 15hp 2str Yamaha outboard (~40kg). Boat is rated for max 25hp motor. Most usage is in inland lakes some of them are big :| with rough water (Lake Simcoe for example). Without wind I could easily get 28km/h speed but when wind gets > 15-20 km/h I am afraid I can snap transom off if I would jump on the waves.

So question is do I need to be afraid or it is not easy to damage transom?

Any thoughts are appreciated.
Thank you,
Dmitry
If you inflate your sib to it's correct working pressure while on water that is 3.5 PSI (get a manometer) don't worry about any transom issues nor bow bending. Is normal to hear some aluminum floor noise while flexing, to lessen, put 3M black tape or duct tape the whole lenght between joining floors. Would recommend to slow down on rough/windy waters because of excesive sib bumping, sitting on the sib interior would be advisable if going out with children.

This aluminum floor 380 surf rescue sib & 25 HP engine has been wave jumping/passing through a 10 row waves every day to reach the surf field area for the past 1 year with no structural problemas/damages at all. Keel & tubes are inflated to 3.5 PSI in shadow before it's launch to water.

Happy Boating
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Old 16 May 2008, 12:26   #8
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Wow! Thanks for the pic's! Looks like 25hp is more fun than 15hp :|
Yes I have manometer, 3.5psi for tubes but 5.8psi for keel according to specs.

Also wondering is it a really bad thing for the engine when prop goes out of water?
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Old 16 May 2008, 13:18   #9
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Also wondering is it a really bad thing for the engine when prop goes out of water?
Not for the length of time you are likely to be out of the water! All you are hearing is the engine over-reving as you're airborne. Put it like this - it's not advisable for safety grounds, but it does happen.
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Old 17 May 2008, 12:07   #10
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Wow! Thanks for the pic's! Looks like 25hp is more fun than 15hp :|
Yes I have manometer, 3.5psi for tubes but 5.8psi for keel according to specs.

Also wondering is it a really bad thing for the engine when prop goes out of water?
Definitely a 25/30 HP 2 strokes is faster, that is why if already investing good bucks on a sib, you should go for the largest HP engine the sib can handle, better to have more and don't need it, rather than less when you need it. Actualy will cost more, but worth the extra investment to gain in performance, transport better cargo loads & obtain best top cruise speed.

When prop is out of the water is for only some seconds, will hear the prop rev higher, nothing will happen being at a medium speed.

Dim, what sib brand is yours ? first time to know that you must inflate your keel to nearly 6 PSI

Happy Boating
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