MATTOO wrote: Mc Skipper, Noticed your chain lengths and sizes. May I suggest that if you have 9 metres in all its a bit more than you may need. The principle with an anchor is the chain is the actual anchor. Even a tanker works the same principle. Although the anchor has a grab factor it's the length and weight of the chain that is actually the anchor. I hope that gives you food for thought. |
Steps wrote: It is a Ratio 1.83 gearbox ratio right? 40hp 2 or 4 stroke? 2S 4.4m hull WoT range 5000-5700 3500 27km/hr (16.8 mph) 4000 33km/hr (20.5mph) 4500 38km/hr (23.6 ) 5000 45km/hr (28 ) 5200 47km/hr WOT (29.2 mph) Prop pitch and diameter ? needed Old alloy prop 11 1/4 x 13 new prop stainless 11 3/8 X 12 pitch
Sry need to keep data all together otherwise have to spend ages going thru back posts / pages digging info out |
Steps wrote: OK lets see what we get... with ratio 1.85 pitch 12" diam 11 3/8. 40hp 2 or 4 stroke? 2S 4.4m hull WoT range 5000-5700 5200 WoT pretty well spot on for normal (??) loaded boat 3500 27km/hr (16.8 mph) 22% 4000 33km/hr (20.5mph) 16.6% high for this weight boat.. 12/13 would be about ideal. 4500 38km/hr (23.6 ) 14.6% high 5000 45km/hr (28 ) 8.8 high 5200 47km/hr WOT (29.2 mph) 8.6% still high 3.5 to 5% more ideal.Good consistant data there.. You would now be in the fine tuning area.. that is for a general use boat all thats needed.. thu if a suitable pro came up cheap..$25/50 worth grabing ..even just for interest sake.. or a good spare. So grip is a little loose.. extra cupping would not do what wanted. around another 1/4" diameter would work well. BUT That will also drop your 5200 WoT lower, estimate around 750 to 100 rpms... still in the manufactures spec, but in my books getting bit close to their limits of loading powerhead right thru the rpm range. As I have said we get the slip right (diameter) them work the pitch. So looking at around a 11 3/4" diameter X 11.5 " pitch with similar cupping as the current prop I dont know what is available in sizing. So lets look at what such a prop would do. current predicted 4000 (20.5mph) 16.6% 4000 21mph 11% slip 5200 (29.2 mph) approx 5200 29- 29.5 3.6-4.5% Bottom line fine tuning would achieve next to nothing.. forget looking for a fine tune prop, the amount of fuel performance would be so insignificant wouldn't be worth the grease or time to change the prop over. I have posted this up.. as always do, doing calculations as I go...hence why above initially suggest, maybe keep an eye open... It also illustrates well that target for a general use boat only needs to be a good ball park...fine tuning beyond that becomes pointless. It is also very nice and preferred to confirm rather than correct a propping..and this is one of the best done so far. As to moving gear around.. it does have its pros and cons. moving stuff foward drops the bow but also increases surface area , drag (in effect makes the boat heavier. If well powered (reserve power) that extra correction in height of the prop will level the boat and the bow wave will still remain just behind the middle of the boat at a good cruise speed. If not well powered If experimenting with moving stuff around to get engine height.. including ppl.. keep that bow wave behind the middle of the hull. If engine doesnt lift then (in smaller boats) lift it |
Steps wrote: Had a similar issue few yrs back on our keel trailer. The boat has brass strip keel. I had , and still have a couple of the alloy rollers. Several of these snapped in the middle. upon removing found that the bushes inserted wher only a 10mm or so inside. This left the center area of the roller unsupported. Hence cracked and broke. I replaced a couple and the centering roller at the back end with cheaper rollers... and used bushes that supported all the way thru...It did not take long for these to chew out like your pic . the end centering roller chewed out real quick. I had kept the broken alloy rollers.. matched up the 1/2s, inserted new bushes that went all the way thru.. 5/ 6 yrs later they still roll well.. A couple others didnt, they had been rather munched... An old post here, yrs ago, another member at the time worked for a plastic company and gave me a couple off cut lengths of the stuff the expensive rollers are made of. I turned these down on the lathe...replaced the broken alloy that where past it... These are still like new yrs on. The rear centering roller bit the bullet and replaced with a more expensive (think read rubber brand ???) And that also has lasted very well, no sign of replacing soon. So 2 things would look at... Are they elcheapo? which by the looks of how chewed and how fast I think so. I reckon they were Boss was out and reception said they had someone in the other with same problem..... And The bushes, if any do they go all the way thru? If not it may mean the rollers where bending , not turning completely.. then eventually not at all and the friction simply sliced into them No bushes just a rod all way through roller close fit And as to "keel sharp" Recon thats BS...just caught out on elcheapo rollers maybe. Absolutely! They may come up with " the side rollers dont support enough weight. He tried that one. That is in corect.. A keel boat on a keel trailer is supported by the keel rollers..the side rollers just keep the boat level. Even a much heavier boat, you should be able to just hand turn a roller before the boat is trapped down to stop bouncing on speed bumps. Good point as height of each roller is adjustable will go through and check similar load on all 3 and not just on back one, of interest rod roller sits on is held in place by a split pin which is folded/spread to stop it falling out - middle roller split pin not folded/spread at all and ready to fall out.... |
Steps wrote: No bushes...they will grab the shafts for sure, not turn and rip. Bushes are less the $2 each, 2 per roller. Not only that the outter collar of the bushes act as a washer (thu should be one there) to also stop the roller moving free .. espec under load. Washers behind the split pins? similar to the above |
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