Not sure this question belongs in this section but here goes...What is the minimum clearance acceptable from the tip of the prop to the hull bottom on a skeg built boat ? in other words how close can you go ?
I've heard 15% suggested as a general rule of thumb, but I've never had that much clearance on my boats. I try to stay in the 11%-13% range from the bottom of the hull, and it has worked great for the boats I've built. So currently the 22" prop has 12.5% tip clearance. I guess you could jump up to a 23" prop and have 9.8% tip clearance, but I would probably stay with the 22" diameter and go with a skewed 4 blade like the DQX. What kind of hp are you thinking of upgrading to and what does the boat weigh?
Gent's I am batteling with a vibration issue on my Duffy 35, Rockasaurus you know the boat, and I am swinging a 26" x 22 " 4 bladed wheel. Power is a 3208 375 Hp and the current prop runs in the lee about 25 rpm at WOT. If I stand over the prop while running at anything over 2150 RPM I get a distinct buzzing/vibration/tone localized over the propeller section of the deck. I currently have 4 1/2" of tip clearance from the hull which works out to be 18%. I am considering changing wheels to a 24 square to increase the tip clearance to 25% with the hope that it would smoothe out the vibration/buzzing/noise I am trying to avoid. So the question really boils down to whether I am chasing the impossible or if another 2" of clearance will make a noticeable difference. Perhaps taking a little pitch out of my current wheel and adding some cup would be another solution. I like the efficiency that comes with the added diameter. Thoughts?
4 -1/2” of tip clearance is plenty, more than enough for a 26” wheel, I would not reduce the diameter. I’ve had 26” props with 2-7/8” clearance run very smooth, so in my opinion your problem is not tip clearance. Is your current prop, bearings, shaft, engine mounts, and couplings lined up and in perfect condition? Is your rudder bearings/packing all tight and steering ram tight?
I sent it out last year for a tune up and some propspeed. According to prop scan it is right on the money. The engine was originally hard mounted with a straight exhaust. I pulled the engine this past winter and soft mounted it with iso-flex mounts and custom Soundown exhaust system. The new system is so quiet I am now hearing noises that I assume have existed for years but were masked by the engine's structure-borne vibration noise. Glad to hear the consensus is that tip clearance is adequate as it rules out another variable. I'll check the shaft alignment again as well as for rudder bearing chatter and report back. I have a feeling that I am chasing the unattainable with regards to making her run like a modern production boat but I don't see why a DE boat couldn't be made to do so.What about the condition of your prop? Is it perfect?