MauriceMynah Posted September 18, 2014 Share Posted September 18, 2014 I'm curious,. firstly... What are the advantages of having a four bladed prop over a three bladed one? How much will one cost and how much to fit? And secondly... I've noticed many hire craft have a metal reinforcement on the bow. How much to have one of those fitted to my Elysian Bounty, and where could I get one? (I make mistakes too you know) 1 Quote Link to comment Share on other sites More sharing options...
Timbo Posted September 18, 2014 Share Posted September 18, 2014 Try the Israeli National Maritime Museum... Failing that Jon has all sorts at Wayford. But for my own curiosity what's with the thrutching accoutrements...looking for a little revenge? : 2 Quote Link to comment Share on other sites More sharing options...
Polly Posted September 18, 2014 Share Posted September 18, 2014 Probably! I just wish to state, for the record, that Brilliant has no bowsprit, so MM can cross her off his revenge list! 1 Quote Link to comment Share on other sites More sharing options...
Polly Posted September 18, 2014 Share Posted September 18, 2014 I saw them doing one at LBBY last year, John. Quote Link to comment Share on other sites More sharing options...
ExMemberBobdog Posted September 18, 2014 Share Posted September 18, 2014 Some years ago I hired one of Mr. Buttifant's beautiful yachts for a week. I was moved to point out to the skipper of a small dayboat, who cut across my course while I was under full sail on Hickling Broad, that the bowsprit was a mighty weapon that would probably go right through his craft. He changed course PDQ. A friend, sailing beside me, took the photo. Quote Link to comment Share on other sites More sharing options...
watershed Posted September 18, 2014 Share Posted September 18, 2014 Think i might get me one of them! Quote Link to comment Share on other sites More sharing options...
MauriceMynah Posted September 18, 2014 Author Share Posted September 18, 2014 In my own defense, it is when I mess up and ram the bank that I was worried about. 2 Quote Link to comment Share on other sites More sharing options...
BroadScot Posted September 18, 2014 Share Posted September 18, 2014 In my own defense, it is when I mess up and ram the bank that I was worried about. Barclays, RBOS or Lloyds? I'll get my coat! Iain. 2 Quote Link to comment Share on other sites More sharing options...
Polly Posted September 19, 2014 Share Posted September 19, 2014 MM was moored and absent when his 'bowsprit experience' occurred. Quote Link to comment Share on other sites More sharing options...
MauriceMynah Posted September 19, 2014 Author Share Posted September 19, 2014 I'm rather hoping Clive (Richo) will know what I'm talking about. It's a sort of shield that wraps round the bow from the top to about 6" above the waterline. Quote Link to comment Share on other sites More sharing options...
Polly Posted September 19, 2014 Share Posted September 19, 2014 Like I said, John, they were taking a pattern for one to be fabricated in s/s at LBBY a short while ago. Is Nyx back at Hickling btw? Quote Link to comment Share on other sites More sharing options...
650xs Posted September 19, 2014 Share Posted September 19, 2014 three blades catch three lots orf water .......!!!! four blades catch four lot s orf water .......!!!!!!!!! but be warned not as simple as thta talk to a prop expert not an ex ...pert but be carfull u can buy of the shelf ..................................... check yer taper on yer shaft etc clearence from skeg and bottom orf the ole boot etc etc and of coarse get the correct " hand" ...........................l/h................................r/h.............. not that dear ............................. search the net ........................???? there are lots of prop manufactures etc talk to ...............................markwell ..peachmants etc local ............go to sillet sonic ...etc etc ask some people who have same hull etc as yer boot and see what they got on her with asame type of engine etc or try a decent correct pitch prop for yer boat secound hand good one with good "ring to it " talk to me i have some props to try ......migth fitt but there is more technical and indepth for whole prop thing ..........................look at turbina ,s props all that time agoo............ummmmmmmmmmmm horse for coarse,s i n reckon a nice five blade surface peirce/ cleaver job for me ........................with 850 hp ................!!!!!!! 2 Quote Link to comment Share on other sites More sharing options...
MauriceMynah Posted September 19, 2014 Author Share Posted September 19, 2014 Mmmmm 5 bladed. I like the sound of that! Quote Link to comment Share on other sites More sharing options...
C.Ricko Posted September 19, 2014 Share Posted September 19, 2014 sometimes people put a piece of stainless on the bows to stop the mudweight knocking the hull Phil at Marine weld will make it for you.. or we will get it made and fit it... 1 Quote Link to comment Share on other sites More sharing options...
Jonathan Posted September 19, 2014 Share Posted September 19, 2014 Maurice, I know nothing about bow protectors, but propeller blades …. More blades is not necessarily a good thing! Propellers are designed to be efficient in transferring engine thrust to the water and so moving the craft forward (and therefore the water backwards). A particular design will have a pitch and curvature optimised for a particular speed, this is similar to gears in a car, some are better for dragging a heavy weight up a hill at low speed, others for cruising fast on a motorway, in both cases the engine rpm is within a similar range. But you are asking about the number of blades, not its’ pitch; obviously, the more surface area a propeller has the more water it can “push against”, and so the more power it can transfer. You can gain area by increasing the diameter or adding blades. But consider the following: You are travelling at 4kts using 1000 rpm. 4kts is 4 x 6080 feet per hour or (4 x 6080)/60 feet per minute or (4 x 6080)/( 60 x 60) feet per second which is about 6.75 feet, or 80 inches per second. 1000 rpm is 1000/60 rev’s per second which is about 17. That means that in one revolution of the drive shaft the propeller had moved about 5 inches forwards (80/17). I can tell that you are already bored and wondering where this is going, so the point is: If your propeller had just one blade then each time it reaches the same point in the rotation (let’s say vertically up (or down)), then it is meeting water that is 5 inches away from where it last disturbed, and pushed-on, the water. If you have a 2-bladed propeller each blade will cut through the water every 2.5 inches, 4-blades every 1.25 inches etc. The problem is that the passage of the first blade has “disturbed” the water, so a following blade is not so effective, and the closer it follows the less effective it is. From the efficiency point of view a single blade would be best … but you might notice the vibration! Consider how the spitfire (wartime aeroplane) design evolved from 2 to 3, 4 and 5-bladed propellers as power and speeds increased over a few years. Sorry if this has been a bit of a lecture, but I think the bottom line is that for cruising gently on the broads it probably makes no difference! Quote Link to comment Share on other sites More sharing options...
ranworthbreeze Posted September 19, 2014 Share Posted September 19, 2014 Hello Jonathan,Welcome to the forum and your first post.RegardsAlan & Tan Quote Link to comment Share on other sites More sharing options...
BroadScot Posted September 19, 2014 Share Posted September 19, 2014 Hi Jonathan and welcome from me also Iain. Quote Link to comment Share on other sites More sharing options...
Jonathan Posted September 19, 2014 Share Posted September 19, 2014 Hello Alan, Tan, Iain, Maurice and everyone else! I've been reading this forum for a few years, "lurking" in the background, and we have been on several holidays on the broads in that time, so I have found several comments and suggestions helpful. I don't consider myself to be an expert on anything ... particularly things that float ... but having recently joined the forum I thought I might be able to help someone else; hence the above. 1 Quote Link to comment Share on other sites More sharing options...
Maxwellian Posted September 19, 2014 Share Posted September 19, 2014 Welcome Jonathan. Good post. Quote Link to comment Share on other sites More sharing options...
Rincewind Posted September 19, 2014 Share Posted September 19, 2014 Certainly helped me, Jonathan thank you...I'd not really considered the 'drag factor' of additional blades through the water. Then again, I'm just not very bright anyway. Welcome, by the way! Quote Link to comment Share on other sites More sharing options...
BroadAmbition Posted September 21, 2014 Share Posted September 21, 2014 We had the similar situation with 'B.A' she originally had 3 x blades which was fine with 34bHP from the trusty perky 4108. Installing a 50HP beta meant we would not be transmitting that power efficiently to the water. We could not get a bigger diameter prop in as there just isn't room, increasing pitch - we would have gone way past the sweet spot and had to much pitch or far too coarse. The Beta will rev to 2'800rpm max sticking with the three blade prop would have meant getting to 2'800rpm very quickly and being 'Under Propped' Too many blades and/or pitch would have meant never reaching anywhere near 2'800rpm and having the Beta labouring constantly and being 'Over Propped' The solution was to enlist one that knows and is well versed in the black art of prop/size/pitch in relation to engine/gearbox type, hull size/profile. Jason at LBBy was our chosen expert. He opted for the four blades and pitch to suit. This resulted in our Beta reaching 2'600rpm and being just slightly 'Over Propped'. He got it absolutely spot on first time - He likes to put this down to his expertise / knowledge - I just think he's a jammy git Since the Beta is now fully run in (Nearly 2000 x Hrs) and since then I have treated the engine and gearbox with 'ZX1' we are now achieving 2'700rpm, burning less diesel and being even quieter/smoother (I did not think that was possible but was happily proved wrong - that's not a first I can tell you) Hope this helps, Griff 1 Quote Link to comment Share on other sites More sharing options...
BuffaloBill Posted September 21, 2014 Share Posted September 21, 2014 Hi Griff. What's with this ZX1? When we bought our car new, it used to slow so quickly when you took your foot off the accelerator that it felt like you'd put the brakes on, but after about 7000mls and was run-in, we got more miles per gallon than when the engine was still tight from new, so Griff's Beta is just a good example of that running process. Quote Link to comment Share on other sites More sharing options...
MauriceMynah Posted September 21, 2014 Author Share Posted September 21, 2014 Jonathan, Welcome and thanks for the info, I'll have a word with Jason when I'm up for a while re a bigger/better screw, and a word at Ricko's for the bow. Get some numbers that sort of thing. Thanks all for the input. Quote Link to comment Share on other sites More sharing options...
Timbo Posted September 21, 2014 Share Posted September 21, 2014 Jonathan, Welcome and thanks for the info, I'll have a word with Jason when I'm up for a while re a bigger/better screw, and a word at Ricko's for the bow. Get some numbers that sort of thing. Thanks all for the input. MM....now that one is wayyyy to easy! 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.