Muzza
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Posts posted by Muzza
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Here's a pic showing wll. Boat specs says wll is 22ft.
IMG_0408.JPGI think that may not be the Cav 26 Bob salthouse bought out his 25 at the same time and that looks more like the SH25
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Harry how does the shaft line look compared to the waterline from memory some of those boats used quite a steep shaft angle?
My last yacht I kept the downward angle down to 3 degrees but once you get over about 6 degrees a lot of energy is wasted in trying to lift the stern of the boat out of the water.
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Harry I always got Doug Peterson and Ron Holland boats mixed up probably because of the fact when Doug started his design career off on a boat called Ganbare he had a young Kiwi boatbuilder working for him called Ron Holland. You can still see a lot of the Doug Peterson influence in Ron's designs. 19ft static Waterline and probably pick up another 3 ft in effective waterline.
You are correct heavy, short waterline boat with fine ends equals pitching. With that amount of power you should still be good for 6.5 knots. a friend has a wright designed tracker with a twin cyl Nanni saildrive in it 13.6 hp and that has top of 6.8knots and will cruise all day at 6 knots on the smell of an oily rag.
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The only feathering props I have had anything to do with are the Max prop which was a two blader,(also available in 3 and 4 blades). These appeared to be more efficient than a folding two blader and virtually the same as a fixed prop going ahead but better brakes than a fixed prop going astern. It is pretty well known that the folders such as Briski's partially close in reverse so reverse performance may be adequate in a small light boat but no brakes on heavier boats. The best of the folders appears to be the Gori. I once worked on a 32ft Shipbuilders launch where the owner decided to import a prop from Australia which was a five blader. The blades were almost finger like in profile and top speed went from 8.25 to just on nine knots. Unfortunately this type of blade showed several disadvantages the first being no punch in a sea way and the second was even worse, no brakes. The first attempt at picking up the mooring resulted in overshooting the mooring, lots of noise and the boat running up on the closest mud bank.
Harry if you know of someone with a hand laser rev counter get him to check the revs on the propshaft in relation to the engine that way you can rule out a gearbox problem.
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Harry and wheels the Cav 26 is or was a quarter ton class, relatively heavy for its length and short on the static waterline probably about 20 to 21 ft but may pick up more length as the stern wave moves out towards the transom (effective waterline). These boats were renowned for pitching. Theoretical max hull speed just under 6.5 knots 16 hp should be more than adequate to achieve this. My feeling is there is something wrong in the prop selected or drive train. 4,400 lb displacement although this was in racing trim, from memory Ron Holland was the designer. Certainly worth getting Henleys to run it through their computer.
From memory these boats had to have quite a steep shaft angle which would also rob efficiency
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Harry with yachts a lot comes into play. Often a propeller is just thrown on and a she'll be right added into the equation. Launch owner obviously spend a lot more time refining things, or should. Displacement vessels such as the H28 for example are known for hobby horsing (pitching) and with the propeller a long way aft on the waterline this rapid vertical movement in waves robs the propeller of efficiency. Propellers in apertures are often compromises and sometimes not good ones at that. Often the diameter is less than ideal typically the fiberglass H28 as first built 40 years ago had a 10hp engine installed so aperture was designed around this so adding additional horsepower often has little benefit as it can't effectively be used. I am assuming that you are using a two blade prop, to get better performance under motor it may be worth considering a three blade and if drag under sail is a concern go three blade feathering. Getting off the subject for a moment a well designed aperture should only be installed into the hull of the vessel and not cut into the rudder especially on long keel boats other wise much of the turning moment is lost, both under power and under sail. One thing I might add which is a personal observation is that the propellers such as the Briski two blade flip flops use a lot of power to push those fat blades through the water. We did a prop change on a townson 34 from two blade folding to two blade feathering both 16 x 10 blades, both had similar blade area. The feathering prop actually enabled the engine to pick up the 300 rpm it was down with the folder and boat speed went up about half a knot.
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Wheels I don't touch the edges of blades unless there is signs of nicks or burrs from hitting submerged objects such as minor debris. I don't have the specialist gear needed to maintain balance I also feel the same holds true for changing the shape of leading edges, for any damage more serious I would send the blade into Henleys or one of the other manufacturers who can make a proper repair. I can remember back in the 70's seeing a friend of my dads screw up (pardon the pun but I couldn't resist it) a good prop on a 34ft launch by hack sawing 3/4 inch off the blade tips to reduce diameter. The vibration just became intolerable over 1800 engine rpm but the owner of the boat was convinced his modification wasn't the problem. I can remember in power boat racing back in the 70's there was a few self professed experts that were cupping the blades with nothing more than a ball pein hammer to get a perceived speed advantage, of course this was done by eye with no accurate way of measuring the results and often the results had less than the desired effect.
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Cavitation has a very distinctive sound and this along with vibration will give you a good indication . After 12 months of use the two bladed prop showed signs of errosion or pitting from the blade tips down the trailing edge. changing to the three blade prop increased tip clearance by the reduction in diameter, no further problems were had.
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Yep. All good there.
Although I was told that adequate tip clearance was important on boats with flat aft sections, on yachts with very acute aft sections, not so much.
Chris no mater what shape the hull is tip clearance is still important we did a displacement yacht once where the two bladed prop clearance was slightly under 10% with this boat only the rudder was causing the clearance issue. we were getting bad cavitation at anything over 2500rpm engine revolutions (3200rpm max rpm, 2:1 deduction) so effectively the boat was only able to use about 60% of the engines power. What does enable you to decrease clearance is decreasing shaft revs but certainly still giving yourself at least 10% clearance. The owner of this boat eventually went to the expense of a three blade feathering prop to increase bite but with a diameter more suitable for the aperture size. The three blade prop was smoother and the boat lost much of the harmonic vibrations but most of all the boat could cruise at 7.5 knot at 2800rpm where before 2,500 gave just under 6 knots
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Changing the reduction gear often doesn't mean a new box it just means changing components in the existing gearbox. As rotation speed of the prop goes up so does propeller slip. Take rotation speed x pitch in inches and you can work out a speed with no slip then find your actual speed through the water and that will tell you how much the percentage of slip there is. If diameter gets compromised a solution might be to move from two blade to three blade feathering to increase blade area and load engine up more.
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Fish. With the boat being that far short of max revs on the engine I would look at a reduction gear change. I have done this on several boats first case a 23ft waterline yacht with single cylinder yanmar 1GM 10. The engine supplier suggested a 13 x 7 Briski two bladed folding prop but engine was 600 rpm short of max revs and max speed was under 6 knots. Engine was showing signs of over loading from 2800rpm. Henleys suggest that data from the boat indicated a 12 x 6 would be more appropriate for that shaft speed. I knew this was the wrong way to go so decided to changed reduction from 2.2:1 to 3.2:1 engine was now under propped so added another three inches of pitch 13 x 9 end result was max speed now 6.6 knots at WOT 3600 rpm being easily reached. With displacement boats you ideally want to keep prop shaft revolutions down to around 1000 rpm. On displacement boats a slower turning prop is always more efficient than a higher speed one. In this case propeller slip decreased from about 32% to about 22%. Henley's took the later figures and then worked out the ideal would have been a 14 x 8 however 14 inch diameter was cutting down propeller tip clearance to the hull to under 10% so the decision was made to stay with 13 inch diameter.
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Jet Raider Quick Cat and Tiri Cat are among the worst but nothing worse that the old mono hull Te Kotuku that was run by Kerridge's to Pakatoa back in the 70's, affectionately known as the Great white wave maker and was responsible for much damage in a time when the authorities didn't care.
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Is this not great news? Now they will be after those pesky ferrries and their dangerous waves!
I think it is a double edged sword you are swinging there, the ferries have there own issues to with boats anchoring in the ferry lane and close to berths at Matiatia and Kennedy Point. I recently got a chance to view the operation of one of Sea Links Ferry barges on the approach to Halfmoon bay one Saturday afternoon. There were numerous small boats fishing in the channel and one in particular was quite verbal when the ferry passed a bit close to him, the ferry was making a final approach to the ramp and no more than about 50meters off when a yacht decided to run the gauntlet and cut through between the ferry and the ramp. The yacht cleared the ferry by no more than 7 metres, I believe the ferries are now fitting camera's to record these type of events events, This yacht would have had plenty of room to pass astern of the barge.
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My thoughts are the actions of a few are going to lead to greater expense for the greater majority of boat owners. To a point licensing I can go along with as some form of education is needed but this probably won't work as well as hitting the repeat offenders where it hurts most, in the pocket. I would rather have an idiot fined than have more rules,regulations and expense imposed on the general boating public. Registration I don't agree with for several reasons 1/ Registration essentially becomes nothing more than a revenue gathering exercise and nothing more. Sure you can identify someone being an idiot but we have had registration on the roads for about 80 years, does registration stop someone being an idiot on the roads? I think not.
Like most people on the roads if you see someone being an idiot the natural instinct is to jump up and down and scream and yell but generally these things don't get reported, human nature takes over and people don't want to get involved in paperwork or interviews. I do believe that the authorities need to spend time policing the more serious misdemeanors rather than fining someone for not wearing a life Jacket even if it is right alongside them.
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I think policing water safety should be taken off the hands of regional and city councils and placed under a central body, not necessarily Maritime NZ either. The councils have shown to be irresponsible in the way policing is carried out and the exercise now is nothing more than money grabbing. As well as a degree of common sense and practicality there needs to be one standard set of rules throughout the whole country. Personally I saw nothing wrong with the original interpretation from Auckland where vessels had to carry them but it was up to the skipper's discretion when they would or should be worn, but of course now even that has been carried a step too far. Friends had their Lotus parked up for the day in Tekouma Harbour. To comply with the new regulations (WRC) they wore their life jackets and left them in the dinghy while ashore. on returning about one hour later the dinghy and oars were still on the beach but the life jackets were gone.The boat then had to return back to Auckland minus four life jackets.
I think the thing that most people have enjoyed with boating up until now has been the fact that people are had freedom to get away from all this kind of nonsense that has been created in the cities and up until now had been trusted with their own personal safety. I do believe that if this trend continues it is the thin end of the wedge, next step will be licensing or registration, not necessarily in that order.
My belief is that idiots are always going to drown just get over it and get on with life.
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You guys are forgetting our fines are put in place to fund the Life Jacket Nazi's budget much as we fund the parking Nazi's budget on the roads. Just another Government orchestrated revenue gathering excersize.
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I remember well the controversy over her selection after 1975 Admirals Cup selection trials, Russ Hoopers S&S design Corinthian was the boat that lost out.
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It cannot go ahead due to the oyster farms in the harbour,By dredging they will unsettle the heavy metalsasnic etc from the gold processing days.Besides it will ruin the quiet settlement as marina holders will insist on a major upgrade of the Thames/Coromandel Rd.
Yes I had been thinking about the marine farms, there are several oyster farms in very close proximity. This was part of the reason that the earlier marina application failed. That site was adjacent to the church on the Thames Coromandel road only a 100 metres or so from the main street of Coromandel. Probably a better proposition would be deep water close to the Tekouma Bay ferry stop (not to be confused with Tekouma Harbour)
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land based disposal has been tried but doing one truck load at a time is an expensive exercise. Farmers were initially keen to use dredgings as fill but the slightly toxic nature with heavy salt content means the dredged material is quite infertile for growing crops or grass also a dump site has to be close to the construction site to be effective. A truck carries may be 7 or 8 tonnes of material a barge such as the westham ones carries maybe 800 tonnes, that is a lot of truckloads.
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The volume of dredging greatly exceeds the volume of the proposed reclamation so inevitably about 50% of dredgings will have to be dumped elsewhere and disposal at sea is the most likely. The current dump site is off Cuvier but it remains to be seen if the authorities will deem this ok for dredgings of this nature i.e. heavy metals and traces of arsenic
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otherwise try a drum pump with a long stem on it 3 to 4 ft should suck up ok once the lift required becomes over 2.5 metres most pumps won't lift. From the looks of the picture the boat appears to be fibreglass so you should be able to get away with washing out with Enviroclean which goes through oil like like last nights curry passes through the system. Enviroclean is a lot stronger than Simple Green..
New prop
in TechTalk
Posted
The cav 26 looks totally different, for its time more performance orientated. The 25 stands out as a Salthouse design, for once Boat Data has it wrong. I think where the confusion comes from both were made by Salthouse's later Cavalier yachts.