Has anyone repowered a 1999 247 Advance from a single 2 stroke to twin 4 strokes? Concerned about weight issue with this model Advance due to the hull not being extended to the end of the transom and the additional weight of the 4 strokes. Thanks for any advice.
Repower
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Sardinia306Bimini
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What you can do first is check weigh gain with the 4 strokes.
Take a photo from the side most level possible and then have some persons with similar or better a bit higher weight standing on the transom and take a second photo just for your records.
This will show you rather correct how much the transom will sink while not moving and show if scuppers and engine bracket get submerged.
Mark a sign at float level with the added weight this will help later as below.
Should it be a lot then you may to a running test but in this case obviously without people standing on the transom,
use for example plastic barrels filled with water near the transom to have transom sink at same depth.
Once you filled the barrels with water till the transom is at same depth run her as you usually do and check for odd behavior.
Biggest problem is often gong over the hump as the lower transom creates a odd water flow to the outboard leading to ventilation issues and without trim tabs she may sliding on her butt instead of getting it up.
If this is the case (as I had on several boats, but not on a GW) then you need first see if you can shift weight bow wards to counterbalance, use more trim tabs and/or a stern lifting propeller.
However, moving from single two stroke to single 4 stroke is not necessarily a problem as modern 4 strokes are not that more heavy as 2 strokes, its more complicated with twins.
Chris
Take a photo from the side most level possible and then have some persons with similar or better a bit higher weight standing on the transom and take a second photo just for your records.
This will show you rather correct how much the transom will sink while not moving and show if scuppers and engine bracket get submerged.
Mark a sign at float level with the added weight this will help later as below.
Should it be a lot then you may to a running test but in this case obviously without people standing on the transom,
use for example plastic barrels filled with water near the transom to have transom sink at same depth.
Once you filled the barrels with water till the transom is at same depth run her as you usually do and check for odd behavior.
Biggest problem is often gong over the hump as the lower transom creates a odd water flow to the outboard leading to ventilation issues and without trim tabs she may sliding on her butt instead of getting it up.
If this is the case (as I had on several boats, but not on a GW) then you need first see if you can shift weight bow wards to counterbalance, use more trim tabs and/or a stern lifting propeller.
However, moving from single two stroke to single 4 stroke is not necessarily a problem as modern 4 strokes are not that more heavy as 2 strokes, its more complicated with twins.
Chris
I had the same hull, but as a 248. Even with the cabin and a single ox66 the bow would rise terribly. That said twin V6 ox66 150s were a factory option, so it can be done. The only twins I would have considered were either Merc 115s or 150s. Both are as light as any 2 stroke offered in the 90s. Everything else is too heavy IMO.
Come to think of it, the 248 was sold with twin 115 Yamahas from the factory.
Don't let the HP of twin 115s deceive you. What matters more is total displacement. Mercs collectively provide 4.0 liters = lots of low to mid range grunt.
Come to think of it, the 248 was sold with twin 115 Yamahas from the factory.
Don't let the HP of twin 115s deceive you. What matters more is total displacement. Mercs collectively provide 4.0 liters = lots of low to mid range grunt.