Engine beds

[chrishelen]

I think i need to renew my engine beds soon,i have some nice oak i can use,but i cant find any reading on the best method of attaching them to the plastic hull,i am going to use apoxy and mat,

do i need to leave a gap between the hull and the oak and use some sort of filler as a cushion or can i use a layer of epoxy and bed the beds down on that and then mat them in?

The engine is a Sabb with nice solid mounts,its not as bad as it sounds, the engine gives off very little if any vibration.

 

[burgundyben]

You should not use epoxy to bond to a polyester hull.

I think if it was me I'd be using closed cell foam and laminating with polyester.

Size of boat and HP will dictate how much to pay up.

 

[chrishelen]

You should not use epoxy to bond to a polyester hull.

I think if it was me I'd be using closed cell foam and laminating with polyester.

Size of boat and HP will dictate how much to pay up.

Good point,

The boat is 27ft,the engine is 10hp.

 

[oldsaltoz]

.
G'day Chrishelen,

If you want to use the Oak I would start by drilling and holes that will be needed and rounding off all the corners, then epoxy treating it.

To be this onto the hull I use a mix of Micro-Fibres and epoxy resin, also mix enough to form a gusset all the way round, us a small fish past jar as a guide to get a neat round finish, then clean up before this stuff cures because it'e a pig to sand after curing, sets very hard.

Stagger the cloth (Not CSM) to spread the loading on the hull, glass in all 4 directions onto the hull.

If through bolting the block, first drill the hole/s oversize and fill with Micro-fibres and epoxy, re drill to required size after curing.

Hope this helps.

.

 

[chrishelen]

G`day oldsaltoz,

great advice as always,

the only reason i am using oak is that i have some offcuts hanging around,would a different type of wood be more suited?i cant wait to get stuck in and just wish the weather would warm up a bit,

thanks
Chris.

 

[markdj]

Epoxy is the best product to use to bind to a GRP hull !!! 2nd best is polyester resin.

One thing to note, epoxy needs temperature, more so than polyester, and don't use epoxy with CSM as the binder reacts with the epoxy - best to use woven roving.


Mark
www.boatdoctorni.com

 

[chrishelen]

Epoxy is the best product to use to bind to a GRP hull !!! 2nd best is polyester resin.

One thing to note, epoxy needs temperature, more so than polyester, and don't use epoxy with CSM as the binder reacts with the epoxy - best to use woven roving.


Mark
www.boatdoctorni.com

Ok,thanks Mark.

 

[oldsaltoz]

Epoxy is the best product to use to bind to a GRP hull !!! 2nd best is polyester resin.

One thing to note, epoxy needs temperature, more so than polyester, and don't use epoxy with CSM as the binder reacts with the epoxy - best to use woven roving.

Mark
www.boatdoctorni.com

Also using CSM will cost more for a weaker job due to the voids in CSM, you get close to 3 resin to one CSM, expensive.

With cloth look for one resin to one cloth by weight.

 

[seasolutions]

epoxy dosent stick to oak al that well, its ok but not as good as a lighter wood which will absorb some resin.

douglas fir would be my first choice here, but rubbiish pine is ok provided you encapsulate well and seal the threads of the bolts,

The tannic acid in the oak wil also atack the steel bolts / taping plates you put in to hold the engine down.

A new boat would proably use PU foam, mild steel tapping plates, and approx 10mm of combi mat (woven rovings with light CSM on the back) over all with the layers tapering out over at least 300mm all round the base of the beds.

the idea here is mainly to use the wood as a former to make GRP engine beds

If using poly resin then I would make the first two and layers 600g CSM, interleave each roving layer with a 300g CSM, and finnish with a 300g csm, then floacoat or bilge paint the lot to protect from oil.

 

[oldsaltoz]

G`day oldsaltoz,

great advice as always,

the only reason i am using oak is that i have some offcuts hanging around,would a different type of wood be more suited?i cant wait to get stuck in and just wish the weather would warm up a bit,

thanks
Chris.

Hi Chris,

As long as the Oak is not showing signs of splitting it should be ok.

You can prime it with a mix of epoxy resin and up to 40% Methylated Spirits, this will thin the resin to allow deeper penetration, the end grain will suck up 3 or 4 times more than other areas.

The gussets will not only help support the timber, but also make glassing a lot easier with no sharp corners. Might even make it easier to clean later.

Avagoodweekend......

.

 

[seasolutions]

tediously technical now:

CSM dose indeed have a lower tensile strength than an equivent weight of rovings.

BUT

over short distances (ie, round the angle between the bed and the hull) it has very good shear strength. ie. the thrust of the prop trying to push the engine and its mounts forwards.

it also has far heigher INTER-LAMINER shear strength than rovings ie, it resistis the forces trying to seperate the layers of cloth and importantly the first layer from the hull.

finally,

it's isotropic (well in two dimentions anyway) ie equally strong in all directions, whereas rovings are only at there best at 0 & 90 degrees to the run of the cloth.

the good news is that by using alternate layers of rovings and CSM you get the best of both worlds ie a composite that is stonger than the sum of it's component parts.

as markdj says, epoxy and CSM dont get on, but luckly for you epoxy resin provides enough inter-laminer strength by it's self due to it's heigher adhesive strength. but it is wise then to combine your 0/90 layers with a few 45/45 layers to get an iso-tropic laminate

 

[oldsaltoz]

tediously technical now:

CSM dose indeed have a lower tensile strength than an equivent weight of rovings.

BUT

over short distances (ie, round the angle between the bed and the hull) it has very good shear strength. ie. the thrust of the prop trying to push the engine and its mounts forwards.

it also has far heigher INTER-LAMINER shear strength than rovings ie, it resistis the forces trying to seperate the layers of cloth and importantly the first layer from the hull.

finally,

it's isotropic (well in two dimentions anyway) ie equally strong in all directions, whereas rovings are only at there best at 0 & 90 degrees to the run of the cloth.

the good news is that by using alternate layers of rovings and CSM you get the best of both worlds ie a composite that is stonger than the sum of it's component parts.

as markdj says, epoxy and CSM dont get on, but luckly for you epoxy resin provides enough inter-laminer strength by it's self due to it's heigher adhesive strength. but it is wise then to combine your 0/90 layers with a few 45/45 layers to get an iso-tropic laminate

Not sure why you would select rovings for this job, Bi-directional cloth would be the correct selection.

Also not the binders in CSM do not dissolve in epoxy so any sharp turn is likely to have an air gap.

And finally, due to the high volume of voids in CSM the job would use a lot more resin and as a result be more brittle and therefore weaker.

Hope this helps.