I have recently become a proud owner of the 1988 Offshore 242G (the model with transom bracket). It's been re-powered with 225 Suzuki in 2017. The boat is much bigger than my previous 20-footer and doesn't sit correctly on the lift. I am looking for info on proper bunks spacing and LCG for this old hull. I have emailed Grady's customer service few days ago, but so far have no response. Searching this great forum, I did find a spreadsheet with data on younger models, but there were no compatible hulls. If anyone here came across such an info or has solved this issue for their 242 with the motor on the bracket - please share! Need to figure how to place the bunks and, most importantly, where the center of gravity is related to the transom with the motor hanging on the bracket. Thank you in advance for any usable info!
Positioning Offshore 242 on boat lift
- Thread starter Arkpov
- Start date
For the bunks, just get them as close as possible to the stringers without landing on a lifting strake. That's easy enough to measure.
For the COG, I wouldn't get too worried about this, either. Consider your COG roughly at the spot where the pinstriping on the side of the boat (also the fiberglass mold detail) swooshes down and turns flatter towards the rear. If you get it about in that area, it should be close enough. The few lifts that I've dealt with over the years... I've always just made an educated guess and it's never been an issue.
For the COG, I wouldn't get too worried about this, either. Consider your COG roughly at the spot where the pinstriping on the side of the boat (also the fiberglass mold detail) swooshes down and turns flatter towards the rear. If you get it about in that area, it should be close enough. The few lifts that I've dealt with over the years... I've always just made an educated guess and it's never been an issue.
What exactly doesn't sit correctly mean?
If you want to determine the stringer spacing that can be estimated fairly well by forcefully tapping the bottom of the hull with a soft faced hammer. If you tap hard enough you will be able to hear a difference when you are over a stringer. Those hulls are pretty thick and exact placement of the bunks is not super critical. The location of under hull fittings may dictate where the bunks can't be and therefore limit your spacing options'
As to the LCG, a decent first guess would be about 70 inches from the transom. Since you have a bracket, yours may be farther aft
Get the bunk spacing to your liking first. After than its just a trial and error by loading the hull in different positions, fore and aft.
If the original boat had the same bracket and a 2 stroke, assuming the new motor weighs more, the LCG will shift aft ( a buoyant bracket can mess up that assumption).
All of this assumes that your lift is sized to handle your new boat.
If you want to determine the stringer spacing that can be estimated fairly well by forcefully tapping the bottom of the hull with a soft faced hammer. If you tap hard enough you will be able to hear a difference when you are over a stringer. Those hulls are pretty thick and exact placement of the bunks is not super critical. The location of under hull fittings may dictate where the bunks can't be and therefore limit your spacing options'
As to the LCG, a decent first guess would be about 70 inches from the transom. Since you have a bracket, yours may be farther aft
Get the bunk spacing to your liking first. After than its just a trial and error by loading the hull in different positions, fore and aft.
If the original boat had the same bracket and a 2 stroke, assuming the new motor weighs more, the LCG will shift aft ( a buoyant bracket can mess up that assumption).
All of this assumes that your lift is sized to handle your new boat.
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Long ago, a consulting engineer told me how he was hired to get the cables that held up a sports arena dome properly adjusted. He hung a rope from each cable and plucked each cable one at a time while measuring the frequency that the cable vibrated at. . He then had the workers adjust the cables tension back and forth until all cables had the same frequency Then he knew the tensions were the same.
Your tensiometer is probably a better approach here
Long ago, a consulting engineer told me how he was hired to get the cables that held up a sports arena dome properly adjusted. He hung a rope from each cable and plucked each cable one at a time while measuring the frequency that the cable vibrated at. . He then had the workers adjust the cables tension back and forth until all cables had the same frequency Then he knew the tensions were the same.
Your tensiometer is probably a better approach here
Assuming all the cables have the same length.
That is an interesting response but I am not sure that length makes a difference. I think that as long as the cables are made with the same specs, material, diameter etc, the natural resonance frequency depends not the tension, not length. My background is in a different discipline so I could be mistaken.
40 years ago I knew the answer to your comment off the top of my head. Now all I know is there’s a harmonic issue and not necessarily a resonant issue. I believe the length weight and tension all play a factor in the frequency of vibration. Plan to dig a little bit and relearn some things.
I'm reading through this and listening to what everyone is saying as I find it interesting -- I don't have the answer, though!Wspliter; It amazes me how dumb I can be sometimes
I woke up during the night and immediately thought about the cable frequency and sad" Duh, think about a guitar string. As you change its length, its frequency changes.
You are spot on and I am in the dunce seat!
But....... regarding the guitar string... which, funny enough, is where my mind was going with this conversation... a guitar string doesn't change length, though. It has a fixed point at both ends and only it's tension changes., right?
What if (again, just feebly trying to take part in this conversation). What if:
---- A 5' guitar string was suspended from the ceiling with a 10lb weight attached to it.
---- Next, take the same guitar string, but 7' in length with the same 10lb weight.
The 7' string would have a lower sound, correct? BUT... and here's where I'm not sure... Do the two strings ACTUALLY have the same tension applied to them? It's the same weight, but because the 10lbs is applied over a greater distance, does that lower the tension?
Maybe this is a bad example? I'm just curious 'bout this!
I'm reading through this and listening to what everyone is saying as I find it interesting -- I don't have the answer, though!
But....... regarding the guitar string... which, funny enough, is where my mind was going with this conversation... a guitar string doesn't change length, though. It has a fixed point at both ends and only it's tension changes., right?
What if (again, just feebly trying to take part in this conversation). What if:
---- A 5' guitar string was suspended from the ceiling with a 10lb weight attached to it.
---- Next, take the same guitar string, but 7' in length with the same 10lb weight.
The 7' string would have a lower sound, correct? BUT... and here's where I'm not sure... Do the two strings ACTUALLY have the same tension applied to them? It's the same weight, but because the 10lbs is applied over a greater distance, does that lower the tension?
Maybe this is a bad example? I'm just curious 'bout this!
In that case they would both have 10 pounds of tension, discounting the weight of the extra string which would add marginally to the weight.
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