Please explain this drawing

[Ron Zaker Jr]

Can someone explain the IMPBA drawing sec 1 Largescale gas revised 2022. What does the 4.75 dimension mean???

 

[Hydro Junkie]

I agree, it is confusing. That said, that measurement is included in rule G.3.a:
Any exhaust system allowed. All boats must meet current IMPBA noise rules. The
exhaust system must exit from rear, side or bottom. The tuned pipe must be enclosed
within full decking from 4 3/4 inches aft of sponson transom to hull transom (Figure 2)
The translation to simple english is that you must have your tuned pipe completely covered by the hull and/or cowl from a point no more than 4 3/4" aft of the sponson transom. IF the exhaust is visible aft of that point, the boat will not be legal to run in competition

 

[Ron Zaker Jr]

I agree, it is confusing. That said, that measurement is included in rule G.3.a:
Any exhaust system allowed. All boats must meet current IMPBA noise rules. The
exhaust system must exit from rear, side or bottom. The tuned pipe must be enclosed
within full decking from 4 3/4 inches aft of sponson transom to hull transom (Figure 2)
The translation to simple english is that you must have your tuned pipe completely covered by the hull and/or cowl from a point no more than 4 3/4" aft of the sponson transom. IF the exhaust is visible aft of that point, the boat will not be legal to run in competition

ok thanks.