Question for GN7

[gn7]

The bottom needs to move around tying it all together will promote stringer fatigue or lifting of the stringers . Constant pounding on the bottom will try to push the motor plate up taking everything with it . Use a drop thru with a block or a recessed bolt on .

I have to agree. I think its more a twisting thing than anything else. You might me able to built the hull strong enough front to back to eliminate most of the bending forces the hull sees, but its near impossible to eliminate the hull twisting. Its why v drive and engine bracing struts tend to have heims on the ends. They can arrest forward and rearward movements without inhibiting the twisting. No matter how stiff you make the stringers, the hull will still twist. About the only thing that can control the hull twist is to lay the sides up taller and heavier, and even the deck.

I know a lot of people say that tying the strut into the stringers is no different than tying the v drive into them, or even the motor plates for that matter, but I only know it has never worked well for a GN. And that Di Marco cruiser is closer to a GN than its a drag flat.
Not all that certain if the motor in my boat is what's moving, or the stringers twisting, but there is definite movement between the motor plates and the stringers. It would surprise me a bit if it was the stringers twisting in spite of the motor plates tying the stringers together, and the twisting wins. Just another reason the engine bracing I usually see use heims on the ends.

[Mitch]

Gn7 Its amazing how much the bottom moves in the V drive area my V drive had a solid 1/8 inch of clearence from the plate to the floor ,after one season the groove in the bottom from hitting the plate was very noticable.The force on my V drive plate is 10 degrees up and forward on one side and down on the other, now tie the V drive to the floor dead center to stiffen that area up just for conversation ,,that energy would have to be displaced somewhere. Funny you mentioned V drives a friend was glassing a strut bushing in his shaft log the other day and my first thought was this . Your taking something that floated thru a hole allowing it to seek its own path seperate from the bottom now its attatched and every time the bottom moves it goes with it ?If nothing else it seems like it would play hard on the V drive output shaft bearing .

[WESTERNAERO]

Thanks guys for continuing this discussion about this, I'm trying to understand why or why not to brace a drop thru. Below are a couple pics I got from some recent GN boat builds that are braced. Hope these guys don't mind me using their pics as examples.
My opinion on the bracing is that, it is there to limit any lateral movement of the strut when turning. I don't feel there should ever be any twisting or torsional forces going on with the strut as the prop shaft is supposed spin freely. Not quite sure I understand how there would be vertical movement on the strut that would put enough force to separate the stringers from the hull, although there is some I'm sure, but not enough to transfer to the stringers through a brace and start any damage. If this were the case with vertical forces a drop thru would be much, much weaker than a bolt on, correct? I do agree with that the motor plate may not a good brace as the torque of the engine could be transferred to the strut and cause some lateral motion. So, continue on, tell me I'm an idiot it's okay, just explain why. Thanks.

[gn7]

Gn7 Its amazing how much the bottom moves in the V drive area my V drive had a solid 1/8 inch of clearence from the plate to the floor ,after one season the groove in the bottom from hitting the plate was very noticable.The force on my V drive plate is 10 degrees up and forward on one side and down on the other, now tie the V drive to the floor dead center to stiffen that area up just for conversation ,,that energy would have to be displaced somewhere. Funny you mentioned V drives a friend was glassing a strut bushing in his shaft log the other day and my first thought was this . Your taking something that floated thru a hole allowing it to seek its own path seperate from the bottom now its attatched and every time the bottom moves it goes with it ?If nothing else it seems like it would play hard on the V drive output shaft bearing .

Your buddy is going to end up tearing the shaft log out of the boat, GUARANTEED!

Thanks guys for continuing this discussion about this, I'm trying to understand why or why not to brace a drop thru. Below are a couple pics I got from some recent GN boat builds that are braced. Hope these guys don't mind me using their pics as examples.
My opinion on the bracing is that, it is there to limit any lateral movement of the strut when turning. I don't feel there should ever be any twisting or torsional forces going on with the strut as the prop shaft is supposed spin freely. Not quite sure I understand how there would be vertical movement on the strut that would put enough force to separate the stringers from the hull, although there is some I'm sure, but not enough to transfer to the stringers through a brace and start any damage. If this were the case with vertical forces a drop thru would be much, much weaker than a bolt on, correct? I do agree with that the motor plate may not a good brace as the torque of the engine could be transferred to the strut and cause some lateral motion. So, continue on, tell me I'm an idiot it's okay, just explain why. Thanks.

Never said there were torsional twisting forces in the strut. The stringers and hull twist. When they do, the bracing, if tied to the stringers, can tear up the bottom near the strut, of loosen the stringers near the bracing.

These two boats, Andrews and Locks have ZERO time on them to speak of. Locks is ZERO, and Andrews has the enduro under its belt. Pretty smooth water relatively speaking. We'll see how it works out for them.
Not telling you not to tie the strut to the engine, telling you I know of no GN currently running that has the strut tied to the engine or stringers.
I have to ask again, when tying the strut to the engine, are you bracing the engine, or the strut?
The other thing I always have to ask when I see this setup is, which came first, the strut placement, or the engine placement. Its just shear lucky that the motor plate and the strut end up like that? I know I can't tie my strut to the motor plate if I wanted to. Would I move either so I could? FUCK NO! So I guess you have to be pretty damn sure where you want that engine when you do this, OR you just stick the engine where it all works out so you can.

[WESTERNAERO]

Your buddy is going to end up tearing the shaft log out of the boat, GUARANTEED!


Never said there were torsional twisting forces in the strut. The stringers and hull twist. When they do, the bracing, if tied to the stringers, can tear up the bottom near the strut, of loosen the stringers near the bracing.

These two boats, Andrews and Locks have ZERO time on them to speak of. Locks is ZERO, and Andrews has the enduro under its belt. Pretty smooth water relatively speaking. We'll see how it works out for them.
Not telling you not to tie the strut to the engine, telling you I know of no GN currently running that has the strut tied to the engine or stringers.
I have to ask again, when tying the strut to the engine, are you bracing the engine, or the strut?
The other thing I always have to ask when I see this setup is, which came first, the strut placement, or the engine placement. Its just shear lucky that the motor plate and the strut end up like that? I know I can't tie my strut to the motor plate if I wanted to. Would I move either so I could? FUCK NO! So I guess you have to be pretty damn sure where you want that engine when you do this, OR you just stick the engine where it all works out so you can.

Really the only reason I thought of tying the engine and strut together were because they are all ready in that location and it would have eliminated the extra brace. And really the only reason I'm even considering using a strut brace is because the inside of my boat hasn't been glassed thicker in the strut area. It's only about .700 thick. Here's a pic of what it would be comparing the 2 types of mounting. I just fear pulling the bolts though the hull in a drop thru.

[gn7]

I understand what you are saying. Thankfully I don't have that concern. My bottom is over 1 1/4 thick between the stringers and the strut block is about 12 X 12 single piece of machined billet, bedded, bolted, and glassed in.
I really can't give you an answer on what you should do. Will Andrews and Locks deal workout, I have no idea. I guess tell. If you are beating the thing like a rented mule it guess it can work with no problems.
I can only tell you that I can show you a number of places in my boat that prove the boat is twisting more than I would have ever imagined. And there is nothing light about my boat.

I see your reasoning, I just can't give you answer what you should do, other than ask if you think you really need to have a drop thru. Speed?

[WESTERNAERO]

I understand what you are saying. Thankfully I don't have that concern. My bottom is over 1 1/4 thick between the stringers and the strut block is about 12 X 12 single piece of machined billet, bedded, bolted, and glassed in.
I really can't give you an answer on what you should do. Will Andrews and Locks deal workout, I have no idea. I guess tell. If you are beating the thing like a rented mule it guess it can work with no problems.
I can only tell you that I can show you a number of places in my boat that prove the boat is twisting more than I would have ever imagined. And there is nothing light about my boat.

I see your reasoning, I just can't give you answer what you should do, other than ask if you think you really need to have a drop thru. Speed?

I just figured if I am going to re-do everything this winter I'm going to make it as strong as possible, I've been known to break shit with the vertical peddle before. The boat actually drives very nice. This whole re-rig thing started because I don't have a down peddle and this boat has the potential to go faster than I've ever had it, but it makes me nervous not having that down peddle so I don't push it. Like I said earlier, I was doing 82 and didn't even realize it because I wasn't even giving it full throttle. So now it's like, what's this things weak parts? and lets fix them now while it all apart. I'm thinking now I should probably get in there and start building up the glass in the bottom. Which ever way I go with the strut I think it safe to say that the bottom should be thicker regardless. Thanks for your time GN, and Mitch.

[steveo143]

On my 19' Schiada, I put a drop thru strut in and made a 2" thick block that sits on top of the clamshell at the rear and is bolted to the motor plate. Seems to work great for me.

[WESTERNAERO]

On my 19' Schiada, I put a drop thru strut in and made a 2" thick block that sits on top of the clamshell at the rear and is bolted to the motor plate. Seems to work great for me.

Can you put up a picture of that?

[SFV2RVR]

Mine is also tied in the the stringers.