Do I need these engine stringers.

[Vidi79]

Hey everyone,

I have been rebuilding a bayliner 2155 ciera sunbridge.

As part of my rebuild process I have been trying to loose weiggw where I can by using light weight materials and omitting things I don't need such as a windscreen wiper and motor. My reason for this is it has a 120hp engine and I reckon it will need all the help it can get to push the boat onto the plane.

The jobs going well but of course as a first timer it has been hard work fibre glassing etc.

Obviously the transom was rotten, however the stringers were only bad for about 3". So I have replaced the transom (took 2 attempts to get the glass right) and the short stringer sections.
Also the engine stringers were rotten and the rear cross member timber that my engine sits on. The long engine stringers seat the bigger V6 and the cross member seats mine.

Can I omitt these engine stringers and just install the cross member timber as that's all my mount needs.

Also when I removed the 3" section of stringers I also cut away the boxing that sat on it, do I need to replace this. I am hoping to leave it off as it gives me a view of what's going off in hidden cavities.
Any help and advice in this will be greatly appreciated.

On the photo you can see my new transom after a removed my first attempt of fibre glassing, just to the left you can see where I have removed the small rotten section of stringer and boxing and the big dark thick lines in the V are where the rotten engine stringers sat.

 

[TANSL]

Can I omitt these engine stringers and just install the cross member timber as that's all my mount needs.

I don´t believe so, I would not eliminate any but in any case, I would suppress some transversal reinforcement before suppressing the longitudinal ones of the engine. It would be necessary to study the complete structure of that area to give a correct verdict. The structure is a set of panels and reinforcements that work well together but can be a disaster if that set is broken.
Try to eliminate superfluous accessories, not the primary structure, or very heavy accessories.

 

[Vidi79]

I don´t believe so, I would not eliminate any but in any case, I would suppress some transversal reinforcement before suppressing the longitudinal ones of the engine. It would be necessary to study the complete structure of that area to give a correct verdict. The structure is a set of panels and reinforcements that work well together but can be a disaster if that set is broken.
Try to eliminate superfluous accessories, not the primary structure, or very heavy accessories.

If it helps I would say the engine stringer length from transom to fuel tank was 800mm and from the actual stringers down to the bottom of the V is about 600mm.
I geuss I could use large ply pads for the longitudinal timber to help give shear strength.
But then I think I may as well copy what was already there as that is of course sufficient.
One of the the reasons I am trying to avoid it is because my transom has been replaced with epoxy biax and I would prefer to do this engine mount section in polyester as I find it much easier to work with when folding round timbers etc. By installing the long stringers I assume I will then have to epoxy it all because it needs to bond to the transom with epoxy.

 

[tpenfield]

You are going to need stringers where they were located. You can reduce weight by using a foam core stringer rather than wood.

However . . . 120 HP is way to little for that boat. You really need the 4.3 V6. I don't think you can get rid of enough weight to make a difference.

So, either do the best you can, while restoring the boat's original structure . . . or get a 4.3 V6 engine to replace the 4-banger.

 

[upchurchmr]

I remember a story about stringers on a power boat.
The company wanted to save money and eliminated them.
During rough water testing the hull broke across, opened the bottom, stopped the boat quickly from high speed, and severely injured the driver.

Don't eliminate the stringers, and make them full length.

 

[Shakey55]

Stringers are there for a reason. Eliminating some will not really reduce boat weight, but will reduce construction strength.

Definitely the 120 hp motor for a boat this size is undersized to say the least.

I wouldn’t be changing construction design for a chance of making the 120 hp the right motor. Repair boat the same as original construction and increase motor size to suit the size boat you have.

In the long run you will be happier.

 

[Ad Hoc]

Can I omitt these engine stringers and just install the cross member timber as that's all my mount needs.

Well,....yes....and ...no!

It is all about the panel size and load paths.

Panel size, if the panel size, which is frame spacing x stiffener spacing has changed and is greater then no!
Load paths, if the whole hull is longitudinally stiffened, and nothing else, adding transverses removes the continuity between long.ts, thus needs to be mitigated.

So, without seeing a structure drawing of what it currently is, and what you wish to propose, can't say for sure...anything is possible to do, but without understanding and mitigation, it is highly possible it will also fail!

Thus, more info please...

 

[Ike]

It has the 4 cyl 120 hp engine? I'm surprised. Most of the ones I have seen have much bigger engines, the 4.3 six for example. I've even seen one that has a 350 in it with over 200 hp. So putting a bigger engine in it would probably only improve it.