There is a slim chance the propeller will work for you, but if it is wrong, then you have another haul out and will have poor performance until then.
I know the Bristol 40 has a waterline length of 27' 6 1/2" and a manufacturers displacement weight of 17,580 lbs. This gives me most of the information I need to run a 'prop-calc' and calculate the optimum propeller for your boat.
However, I see from line drawing the Bristol 40 is a full keel with rudder and the propeller is in an aperture between the keel and the rudder. Do you know what the maximum size of propeller you can fit allowing for the 15% clearance rule? Alos, above the manufacturers displacement weight, what weight of personal equipment do you estimate is added to this over the years.... Let me have this information and I'll run a prop-calc based on your new engine. Also, knowing the original propeller specs. will also help and I can run a reverse 'prop-calc' to see how this performs.
Here is the propeller calculation I promised you...
First I allowed the program to work without a propeller restriction, so we had optimum answer.
The results Propeller 18x10 3 bladed gives 6.8 knots with 44% slip and 46% efficiency
Fixing the propeller diameter to allow for the 15% rule Propeller 15x13 3 bladed gives 6.2 knots with 61% slip and 36% efficiency
Now, it is possible to get away with a 10% of propeller diameter as tip clearance where the propellers efficiency is degraded due to diameter limitations, which is certainly the case here.
Fixing the propeller diameter to allow for a 10% rule Propeller 16x12 3 bladed gives 6.5 knots with 56% slip and 41% efficiency - This is much better.
These results are guidelines as sizing propellers using known parameters gets us close to the optimum, but expect to do a little 'tweeking' if necessary. Ultimately, when operating under WOT (wide open throttle) your engine should operate within 200 RPM's of the manufacturers specification. The Beta Marine BV1505 max. RPM's are 3,000. If you can achieve this, then you are near to an optimized propeller.
Bob
(FYI 200 RPM's equates to about 1" of propeller pitch)
I cannot recommend the use of a 14x13 3 blade propeller. It will work, but it is a very inefficient propeller. You will not have anywhere near the boat performance that you should have but it will keep you going for the next month or so.
Mike, perhaps you could run the calcs for me and my boat also.
The Panacea is a 20,000 gross weight sloop with fin keel, skeg hung rudder and an official water line of 30 feet but with the reverse stern that sits down underway, the real water line is closer to 35 feet. As you know I installed a new BV1505 this last spring and put 1800 hundred miles on it this summer cruising in the beautiful northwest. It worked wonderfully the entire time.
I have been running a 15x13 three blade prop and getting 6 knots at about 1600 rpm, burning an average of just under 0.5 gallons per hour. If I push it to 2200 rpm I get boat speed of about 7.2 knots. I have a Volvo 17x11 two blade folding prop for my saildrive that I'm considering installing the next time I'm hauled out (or if I want to dive and do it under water). Will that prop do well for me or should I consider a different set of blades?
I looked up the information on your engine (K16435) and I didn't see any reference to your existing transmission ratio for your Volvo 110S saildrive, it's either 1.66:1 or 2.15:1
I've had to assume that you have a 2.15:1 ratio for the purpose of this prop calc. If this is this is the case a 17x11 two blade will leave you grossly under propped. I think that you would be nearer 17x15 or 17x16 two blade.
I must have the 1.66:1 ratio saildrive as when I had the folding prop on before I changed engines from my old Volvo 35 hp it would push the boat at 6 knots routinely. I understand that when the engine was new it would push the boat 7+ knots with the original prop which was essentially the same (I think). Anyway, I had the current folding prop on for a while and took it off because the old engine tended to overheat and I put on the 15x13 3 blade thinking it would help and it did, a little.
Anyway, assuming I have the 1.66:1, is the 17x11 2 blade OK? As noted in my first message, I ran this summer at significantly less than the 3000 rpm that my engine is rated because it would not turn above 2300 rpm.
If you have the 1.66:1 ratio, I think that you will want a 17"x 8" two blade propeller. This will allow you to get the full 3000RPM from the engine and all the HP that it can develop. With such a long line I think that you will be able to cruise at close to 7 knots.
