clydeoutboardservices
Active Member
lol my honda 90 pushing a 1.5 ton boat uses less than £15.00 for a full day out on loch lomond and travelling over 10 miles so enjoy your engine and dont worry about the fuel.
Dave
Honda BF20 outboard max rpm?
- Thread starter Deefor
- Start date
lol my honda 90 pushing a 1.5 ton boat uses less than £15.00 for a full day out on loch lomond and travelling over 10 miles so enjoy your engine and dont worry about the fuel.
Dave
VicS
Well-Known Member
Deefor
Well-Known Member
So that is 10 x 7⅝ inches in place of 9¼ x 10 inches
That should get the revs over 5,000 with no problems. The increased rpm will allow the engine to develop more power so it should get the boat on the plane more quickly and push it a bit faster too.
Going to use more fuel though
Full displacement boat I'm afraid Vic, Viking 20
. Only used on inland waterways but we were looking for a bit more ooomph say when crossing Breydon Water and punching the tide on the Broads (when we get there).With the current prop running at 2200-2400rpm, we're burning only 1lt of petrol per hour and that's with a new, tight engine at only 35 hours use.
Honda dealers on the Thames, all two of them, both say that the BF20 should have been supplied with the high thrust prop when fitted to the V20. Viking should have known better when they fitted the engine but then they buy their Honda's from the south coast where the supplying dealer just leaves the standard prop on.
There's a good quote from a Honda dealer up on the Great Ouse - "When an outboard is fitted to a boat with a heavy displacement hull it can benefit from a different prop to the standard one supplied from the factory. Honda offer a "power thrust propeller" kit that is a larger diameter prop with enlarged blades, this is much better to suited for pushing a heavy boat through the water rather than speeding along in a RIB or dinghy", which just about sums up our type of crusing.
Using the industry standard calculation, I took this from another forum which seems to make sense -
The Viking 20 has a full displacement hull. Its speed is therefore dependent on its waterline length.
its speed therefore = the square root of WL X 1.5 so say 19ft WL
= 4.358 X 1.5 = 6.53 MPH.
You will push the boat faster up to about 8 MPH but you will push a huge wall of water infront of you and burn a huge amount of fuel.
If you want to go fast you need a planing hull that goes across the water not through it.
At least now I've got a spare prop should I ding one of them
.
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JRR
New Member
Well done for sticking it out and leastways getting some satisfaction from the situation [ satisfaction inversely proportional to the number of £ notes exchanged.] Perhaps you should consider having a bulldog painted on the bows!
Hope the new prop brings the engine up to the expected performance and Breydon Water proves to be a pussycat under such lavish power. When we crossed it last month there appeared to be more shore frontage visible than I recall on previous crossings. We were on a 40ft oil burner which plugged its way steadily across, yours I imagine, despite its displacement hull should be somewhat zippier
Look forward to your report back after your first crossing with the new outfit.
Cheers.
Hope the new prop brings the engine up to the expected performance and Breydon Water proves to be a pussycat under such lavish power. When we crossed it last month there appeared to be more shore frontage visible than I recall on previous crossings. We were on a 40ft oil burner which plugged its way steadily across, yours I imagine, despite its displacement hull should be somewhat zippier
Look forward to your report back after your first crossing with the new outfit.
Cheers.
landlockedpirate
Well-Known Member
Deefor
Well-Known Member
Took the boat out on Saturday with the new Honda 4 blade ally high thrust prop (10 x 7 5/8) and the first thing we noticed was that we needed to do 400rpm more to achieve the same river speed as measured on the GPS. This was to be expected and the engine now revs to 4800rpm. Two things we didn't expect though:
1) We entered our first lock on the Thames with the new prop fitted and due to the wind, a bit faster than we would normally. I put the engine in reverse and gave it a few revs (as I used to with the old, standard prop)and it was akin to throwing an anchor over the stern. These high thrust props certainly do bring the boat to a halt pretty damn quick.
2) Between 2200 and 2600rpm, there was a screeching sound from the engine. This wasn't the engine itself as, out of gear, the noise wasn't there. I know I didn't overtighten the new prop as I torqued the castle nut as per the Honda owners manual. Then, by mistake, we went through some shallow water and heard the prop hit the soft, stoney river bottom. Strange, but after this incident, the screeching stopped.
Now the boat is out of the water and back on the trailer, there's minor damage to all four blades - the once smooth blade edges are now a bit rough and could be filed smooth but, as the prop is now so quiet (as one would expect), I'm inclined to just leave them as is. Any thoughts as to why the new prop would screech?
All in all, more than happy with the new prop.
1) We entered our first lock on the Thames with the new prop fitted and due to the wind, a bit faster than we would normally. I put the engine in reverse and gave it a few revs (as I used to with the old, standard prop)and it was akin to throwing an anchor over the stern. These high thrust props certainly do bring the boat to a halt pretty damn quick
.2) Between 2200 and 2600rpm, there was a screeching sound from the engine. This wasn't the engine itself as, out of gear, the noise wasn't there. I know I didn't overtighten the new prop as I torqued the castle nut as per the Honda owners manual. Then, by mistake, we went through some shallow water and heard the prop hit the soft, stoney river bottom. Strange, but after this incident, the screeching stopped.
Now the boat is out of the water and back on the trailer, there's minor damage to all four blades - the once smooth blade edges are now a bit rough and could be filed smooth but, as the prop is now so quiet (as one would expect), I'm inclined to just leave them as is. Any thoughts as to why the new prop would screech?
All in all, more than happy with the new prop
.Deefor
Well-Known Member
VicS
Well-Known Member
Screeching I dont like the sound of. Definitely something to investigate I'd think.
Any signs of contact between the prop hub and the housing in front of it.?
I hope you have not done any damage hitting the bottom.
Rather interested to know what benefits the new prop brings
20 Hp I'd think was more than enough power to drive a 20 ft displacement hull at its max theoretical speed even with the "standard" prop.
10 hp ought to be enough.
You have increased the revs for any given speed through the water but doesn't that simply mean its noisier and uses more fuel. Viking may have deliberately stayed with the standard prop for those reasons.
Any signs of contact between the prop hub and the housing in front of it.?
I hope you have not done any damage hitting the bottom.
Rather interested to know what benefits the new prop brings
20 Hp I'd think was more than enough power to drive a 20 ft displacement hull at its max theoretical speed even with the "standard" prop.
10 hp ought to be enough.
You have increased the revs for any given speed through the water but doesn't that simply mean its noisier and uses more fuel. Viking may have deliberately stayed with the standard prop for those reasons.
Lakesailor
Well-Known Member
I'd be interested to know your reasoning there.
This is a displacement hull.
I run my small displacement boat at a bit over tickover most of the time and never exceed half revs when I am doing a touch over hull speed.
There is absolutely no need to gear the prop to achieve full revs at that speed. That would be rather like driving your car around in town in 1st gear all the time so that you were able to maintain 6000RPM.
If a boat needs 10hp to achieve hull speed there is no point gearing it to run at full revs/20hp.