LB26

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fallguy1000
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Re: LB26

Post by fallguy1000 »

Engine weight?
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fallguy1000
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Re: LB26

Post by fallguy1000 »

Assuming an engine weight of 771 pounds, a 4" error is 4/12*771 or a 257 foot pound moment forward. Or 350kg • 0.1m or 35kgm,

This moment can be offset by placing an offsetting weight aft. If we assume the center of mass of the boat is say 3m from aft, placing a 12 kg mass near the transom would be offsetting. This would not be done until the boat is sea trialed.

35kgm moment forward
35kgm moment aft @ 2.95m = 11.86kg

I cannot speak on the engine mods, but this is how to tweak the engine mass issue, based on my crude assumptions.

It can be done with lead or 12 bottles of wine or so..
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fallguy1000
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Re: LB26

Post by fallguy1000 »

Jacques-you available? Les has a question about engine stuff a day or two back.. And I buried the question twice now! so am mentioning it.
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jacquesmm
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Re: LB26

Post by jacquesmm »

Sorry but I had no internet access yesterday.
First, the engine mounts: your drawing looks fine.

Shaft log:
I don't know where that difference in the shaft log position or length come from but to move the engine forward 100 mm will not make a noticeable difference.
It may not be necessary, you can also trim the shaft log. I don't see any picture and may not understand the problem. Can you please post a picture of the shaft log inside the hull?
The shaft log has to be long enough to allow the stuffing box or shaft seal hose to fit over it. It does not have to stick out more than that. During the design, I locate the engine and shaft first not only for weight but also for clearance all around: will the bell housing fit or be too close to the bottom? Will the oil pan be high enough to reach the drain plug etc. ? Do I want a oil change tray under it? Once I get the engine and prop where I want and at the proper angle, I draw the shaft log, not the other way around.
You do not want the coupling to be too close to the stuffing box. You need some space to change the stuffing or, if you use a friction ring, you want enough room to change it without pulling the engine. Think that you need sufficient space to slide the shaft back and pull the coupling, let's say 10 cm between coupling and end of stuffing box or shaft seal.

Engine location: if you have to move it forward (may be not) consider what happens at the top. Will it fit under the sole? Is it not too close to a bulkhead: you need access to the water pump, it's in the front on that engine.

Post a picture of the shaft log please, maybe with your engine template.

I may not reply right away. I am in a region that was affected by tornadoes a few days ago and the internet is spotty. The weather forecast for tonight includes more tornadoes. I am in a safe place but the internet may go down.
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les2021
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Re: LB26

Post by les2021 »

Jacques / Dan

Apologise for the slow response, we have had no internet on the island since Thursday.

Please see engine mock up pic attached, it leaves about 50mm clearance under the engine at the coupling end, the top of the ply is the engine. The position of the engine on my mock up leaves 100mm between the the stuffing box and the coupling.

Another question.... once the stringers, main frames are in how do you treat the hull ? most boats look like they have had a coat of paint ?

Cheers

Les

Les
0563DDC7-4405-4DF4-8355-6205BA196EF0.jpeg

fallguy1000
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Re: LB26

Post by fallguy1000 »

Yeah, you want certain areas to be ez to clean. I recommend a minimal fairing effort in lockers you want to wipe clean. It need not be perfect, but you also don't want to cut your hand or rags cleaning an oil spill, for example.

So sand with 40-60 grit and fair one time lightly if needed and sand one more.

For bilge paint, oil based enamels are my preference. But pre catalyzed water based epoxies are also great.

Bilge paints tend to dry poorly after application. They sit in a locker or low spot and the fumes or moisture from waterbornes sits above the paint and the next day when you want to work; the damn stuff is still wet. So, use a fan to move air after painting.

Do NOT paint any areas that will get epoxy putty or tabbing. None of my watertights were painted inside. A few lockers were and some were not. I expect the lockers may need it later. Enclosed bilge spaces don't need it.
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Fuzz
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Re: LB26

Post by Fuzz »

Not sure what you have planned for the shaft stuffing box but you are going to need a couple feet between the end of the shaft log and the tranny coupling. Make sure you have working room and access or you will hate yourself later.

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Re: LB26

Post by jacquesmm »

I agree with Fuzz, you need room there. Maybe not a couple of feet but as I wrote before, enough to slide that stuffing box/shaft seal on the tube, repack when needed, change the coupling etc.
I would say at least 6" of shaft, maybe more. a couple of feet as Fuzz say is probably from where the tube sticks outs to the coupling but before we discuss dimensions, are you certain that template is correct? It looks very wide at the bottom.
If yes, you should slide the engine forward. I don't see enough clearance in case you have to move sideways during the alignment but that is because the bottom is so wide. I don't have the Nanni diesel of drawings here but that oil pan is not that wide, neither is that transmission.

I'll be back in my office next week and will draw a sketch to ask for dimensions. For example, when you put your finger under the tube and slide it back to where it touches the hull, what is the distance from there to the end of the tube? We may be limited by the width at the bottom but that tube looks quite long.
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Fuzz
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Re: LB26

Post by Fuzz »

I was thinking if a stuffing box like this were used. https://retmarine.com/shop/self-alignin ... -sa-series
Of course they make other styles like drip-less or bulkhead solid mount and they will be different lengths. Might be best to have the stuffing box in hand before locking the other parts in place.

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Re: LB26

Post by jacquesmm »

Fuzz wrote: Wed Apr 06, 2022 5:54 pm Might be best to have the stuffing box in hand before locking the other parts in place.
Yes.
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