3/4” Star board under motor mounts

[stormalong]

Originally Posted by sinnerman

G10 doesn't rust/corrode in a saltwater environment.

The whole engine is iron and steel.

If someone is that worried about rust use aluminum as I recommended earlier in this thread. Aluminum (or steel) can be done in laminations to build up the desired thickness. That's what I did when installing my Beta 50 over 20 years ago. Steel is easy to paint. If your engine space is so wet that rust is a problem there is something wrong with your boat.

G10 is expensive and harder to work with.

[Boatwright]

Originally Posted by rslifkin

I'm pretty sure Starboard is susceptible to creep, so over time it may compress slightly under sustained weight and cause things to become loose or throw the engine alignment off. Because of that it's probably not the best choice.

Starboard is squishy stuff -- bad idea.

For wood shims: Ipe which is now available as a wood patio deck material. Very rot resistant, doesn't split too easily.

For composite: Mcmaster-Carr sells a heavy duty "red fiberglass board". 1/32" - 1" thick. This stuff is nearly bullet-proof.

[GrowleyMonster]

I would use 316 Stainless Steel. It's the right thing to do, if you are concerned with corrosion and compressibility. Thermal expansion should not be an issue as the dimensions of the part will be small. I am spoiled by having a mill for making parts like that for myself, but seriously you can cut and drill it with very ordinary tools like angle grinder, drill press, even a hand drill if you have a good eye and a steady hand, and a good bench vise. Take your time. "Peck" drill, use plenty of oil or water to keep the bit cool. Use fresh cutoff wheels that have never been used for carbon steel.

You WILL have to go through a few rounds of adjustment before everything settles in and your alignment stays put, no matter what you use. Learn to do your own shaft alignment. You will be glad you did.

[stormalong]

Originally Posted by GrowleyMonster

I would use 316 Stainless Steel. It's the right thing to do, if you are concerned with corrosion and compressibility. Thermal expansion should not be an issue as the dimensions of the part will be small. I am spoiled by having a mill for making parts like that for myself, but seriously you can cut and drill it with very ordinary tools like angle grinder, drill press, even a hand drill if you have a good eye and a steady hand, and a good bench vise. Take your time. "Peck" drill, use plenty of oil or water to keep the bit cool. Use fresh cutoff wheels that have never been used for carbon steel.

You WILL have to go through a few rounds of adjustment before everything settles in and your alignment stays put, no matter what you use. Learn to do your own shaft alignment. You will be glad you did.

GrowleyMonster, You must be joking.

[GrowleyMonster]

Originally Posted by stormalong

GrowleyMonster, You must be joking.

Actually, no, I am not. 316 is fairly resistant to marine envorinment corrosion and while it is not nearly as easy to machine as 7075 or 6061 aluminum, it isn't too bad if you are patient. SS isn't just for multimillion dollar shops. Shade tree machinists and tinkerers can use it, too.

Of course you can also just do a layup of mat and resin. After all, it is bearing on a fiberglass hull, anyway.

[s/v Jedi]

The G10 bar linked above is cheap and one day shipping.

Yes it is hard, which is what you want. I cut it a lot a use an old dull thin kerf saw blade in my table saw, cutting one turn of the depth-wheel every pass. I did a lot of 1-1/2” thick material a while back and it was a breeze.

Oak from Home Depot is probably red oak, a very bad material as it’s end grain soaks up moisture like nothing else. White oak is okay when sealed.

Not really anything against G10. When you buy bar of the correct thickness and width you only need to cut the right size pieces off it which can be done with a manual hacksaw and a couple blades. I also have special carbide tipped blades for my jigsaw.

[Wolf Pack 2]

I think starboard would be perfectly fine but if you need piece of mind, they also make it in teflon which is even more durable than starboard. You can’t even sandpaper that stuff. I’ve used it on my trailer bunks. I’ve seen small grooves on the exposed starboard sections but never on the teflon sections.

[thinwater]

Originally Posted by stormalong

I don't know where this fascination with G10 comes from. Aluminum or even steel are the most durable and least expensive solutions.

Or structural fiberglass sheets for 1/2 the price. Still stronger than anything else on the boat and more than 20 times stronger than oak. G10 is formulated for flame retardant and electrical properties that have nothing to do with boats. It's really made for a different purpose. Structural fiberglass plate from McMaster Carr actually has a higher impact rating than G10.

I've used G10. I don't see that it has any advantages over structural grade for most boat applications, and it is more brittle and harder to work.


Sorry, but it's really funny that the forum reflex is always G10. Sort of like using teak for all wood applications, even when it isn't the right material.

[Iron E]

Originally Posted by GordMay

Delrin has a compressive strength of 5,200 psi.

Interesting. IPE has a compression strength of 13,500.

[s/v Jedi]

Originally Posted by Iron E

Interesting. IPE has a compression strength of 13,500.

Interesting. G10 is 65,000psi

Starboard has creep.

[GordMay]

Comparing "G10" and "FR4" Material Properties:

When discerning the difference between G10 and FR4, it’s crucial to consider their material properties, which are pivotal in determining their suitability, for specific applications.

- Tensile strength: FR4 and G10 boast a tensile strength of 65,000 psi — excelling in resisting stretching forces.
- Compressive strength: G10 takes the lead with a compressive strength of 40,000 psi, while FR4 follows closely at 38,000 psi.
- Flexural strength: G10 exhibits a higher flexural strength of 75,000 psi compared to FR4’s 60,000 psi, making it more resistant to bending forces.
- Bond strength: G10 holds an edge with a bond strength of 2,200 psi, whereas FR4 offers 2,300 psi.
- Shear strength: G10 boasts a shear strength of 19,000 psi, while FR4 excels with 21,500 psi.
- Hardness, M scale: G10 scores 110 on the M scale, whereas FR4 scores 115.
- Specific gravity: Both materials share a specific gravity of approximately 1.8 to 1.85.
- Flammability rating: FR4, as a flame-retardant material, carries a flammability rating of 94V-0, offering enhanced fire resistance compared to G10, which has a 94HB rating.
- Maximum temperature: FR4 and G10 can endure temperatures up to 284 degrees Fahrenheit.
- Water absorption: G10 demonstrates slightly higher water absorption at 0.11 than FR4’s 0.10.
- Izod impact strength: Both materials showcase an impressive Izod impact strength, with G10 and FR4 registering 14.00 at 120 degrees Fahrenheit.

[stormalong]

This is not rocket science and space age materials are not needed. Everyone seems to be overthinking and over engineering these simple spacers.

A beta 50 weighs about 450 pounds and has four mounting feet. The torque and thrust are not astronomical. I'm too lazy to do the math but it is not a huge number. The spacer in under a compression load. Almost any dimensionally stable hard material; wood, steel, aluminum, fiberglass will handle the stress. But there is no need for a G10 epoxy fiberglass product. The engine itself in primarily made from cast iron and steel. It is painted and the paint will protect from rust for many years. The same is true for painted steel spacers, the least expensive solution. Or save the effort of paining and use aluminum.

Apply the KISS principle and save your thinking for the difficult stuff.

[RonaldL]

What I miss in this discussion is the purpose of the elastic mounts: vibration damping (in better words isolation).
Strength is the least of your worries.
You should think of the engine being the vibration source.
You do not want to see those vibrations in the hull.
Therefore you need to try to get a high as possible isolation.
The upper part of the mount vibrates with the engine.
You want the lower part of the mount (and hull) to be vibration free.
That is only possible when the hull and lower part of the mount is stiff and has a high resistance against vibration.
Prerequisite is a stiff hull and base. And a stiff installation of the lower part of the mount.
You do not want to introduce softness by mounting an extra block of matter between the bottom of the mount and the hull.
It also depends on how to attach this block to the hull and/or to the mount. Is the bolt attaching the mount to the hull going through the block. Than this is a longer bolt than in the situation that the bottom of the mount is attached directly to the hull. You introduce softness here resulting in a lower vibration isolation efficiency. Meaning more vibration in the hull.

One of my teachers in vibration technology said: when vibrating, everything gets jelly.

[rslifkin]

On the topic of aluminum spacers, that's what the builder of my boat used to get the engine mounts at the height they wanted in install. 38 years later and the un-coated aluminum is doing fine.

Realistically, any material with enough compressive strength, no creep, and that won't rot will do the job. Use what you're used to working with or can get and cut readily.

[Iron E]

Originally Posted by s/v Jedi

Interesting. G10 is 65,000psi

Starboard has creep.

Wow... That's the shizz you want.
Bonus: G10 is also 100% rot resistant