Trojan Boat Forum

I should add the circumstances that led me to dealing with the prop. I'm in Philadelphia, and there are two destinations for us. The Chesapeake Bay, which is about 45 miles to the closest entry. And the Delaware Bay and Atlantic, which is 60 to 80 miles respectively. I'm usually in the river or the bay, so not in rough seas that often.

So my problem is that on route to these destinations I can only do an average of 12 to 14 knots. I'd love to get closer to 20 to 22 knots or faster, which I thought this boat would do. I'll never reach those speeds in any case if I can only get it to 3k rpms, so that's where I was coming from in terms of need.

ready123

Fact 4 blades have more drag there for are less efficient . true in many cases 4 blades give more lift , but not always so it not a fact ,
and what makes more lift good ? on my boat it would be a bad thing as I have a bow that rides too low at speed . the same boat as mine with the same engine (15 hp more ) is slower across the board on plane only difrence is his 4 blade props , they have scan and tweeked but still not close . and yes he burns more fuel . and thats a fact

I don't think you understand engine loading and fuel burn at all and sure do not understand fuel burn vs speed

4 blades have there pros and cons just like 3 blades

I thought most f32s came with 3 blades ? I know my F36 and f30 did .

bacjk to where it started

The post started with a posting on the right prop for a boat to increse speed . I still feel the 3 blades will be the best in his case , as you said 4 blades slowed your boats cruse down .

wet wonder , sorry we have gone of track . you need to try that 13x10 prop and see what happens even ready 123 agrees on that

if you bottom is clean incl thr running gear you engine should be turning 4000 -4200 if you can't turn up that high with the 13x10 then you could have a engine issue . change the prop and lets what happens I think most every one agrees on that . that prop will be close where you have a good base line on what size prop would best . It could very well be the 13x10 rember that prop can be ajusted for pitch or cup if needed .

prowlersfish wrote:Fact 4 blades have more drag there for are less efficient . true in many cases 4 blades give more lift , but not always so it not a fact ,I thought most f32s came with 3 blades ? I know my F36 and f30 did .

So these guys are wrong?
http://www.hillmarine.com/MercruiserAlpha.html
and these guys at bottom of page:
http://www.marineprop.com/propinfo.htm

Re your comment of the other boat like yours with 4 blades, what are the chances that his 4 blades are incorrect for the boat (pitch/dia wrong). Why does your boat run bow down? I doubt that is by original design, something has changed to put more weight forward. Trim tabs do not correct this?

All I can say is my owners manual has a dealers insert of equipment list and it says 4 blade propellers, 3 blade spares on the top line. I have no idea what the factory did....
When I go up next week I'll look at my prop sizing of both to see the difference.

You guys are making my head hurt.

The prop is the final link to transferring the power of the engine to the water. You want the prop to limit the rpm’s of the engine at WOT to match the recommended specifications.

Our boats, like many of us, has gotten heavier with age. We’ve had many years to add things. Most of us have stuff packed into every nook and cranny. The boat has had years to suck up water. We have many coats of bottom paint. Our engines are not brand new and the hull is not perfectly clean. If we have the same pitched props that were on the boat when it was new, we shouldn’t be surprised if the engines don’t reach the recommended RPMs.

Ya, in a perfect world we could have the props tuned to the boat. For a grand we could have an expert re-pitch the props to match the boats performance, but I’m not doing it. I’m not made of money, and am happy that the boat runs as well as it does. I rarely run the boat over 3000 RPMs, and I don’t put that many hours on it a year. If I was running through a tank or two of fuel a week I would do everything I could to make it more efficient.

My boat came with 20x21 three bladed props. I bought a brand new set of 20x21 props on eBay for $250. Ya, that was for both and were exactly the same as what was on the boat. Before I put them on, I hade them scanned, and keep the old ones for spares. If I were going to buy new props at retail I would have dropped back a bit to boost the RPMs, but for that price I’ll live with being a little over propped.

u know what i want is the be able to shift my boat ...like get it up on plane then shift the tranny into second and lower my rpms but keep the boat out of the water......but i also want .....well alot of things lol

ready123 , as fas the other trojan like mine , has worked with sevral props shops trying to inprove the numbers but still can't get near mine with the 4 blades , as far the bow running low rember I am running diesels that are heavier the the gas engings it came with . trim tabs can only lower the bow not raise it . the bow only starts to get low at 24 knots plus ( will plow at 27 ) so its no big deal as I cruse 22-24 knots
the only time I use the tabs is around 15 knots and thats is not a speed I run very often .

as far as your link they are I/O prop sellers ( we are talking inboards) do you belive every thing a salesman tells you ? I am going buy what has work for for me and yes I have had boats that do better with 4 blades ,heavy boats with slow turning safts

Like I said what works for you works for you , what works for me works for me , but we are not looking for the same thing . their is no perfect prop for all condtions

now now boys..lol as for a perfect prop...i wish there was....one for low end hole shot then it would somehow change for top end....actual i think i have seen somewhere they hav them for i/o plus the prop for the beginning of the season doesnt work so well at the end...ie crap on the bottom and the 3 tons of crap that has somehow ended up inside the boat lol....the guy said he had a spare in the boat he should try that...if it is hard to change after sea trail then he should what every an indentical boat runs...or he can just keep trying them.....one my commodore it had one 260 i/o that i repowered to twin 260s it was fun trying to find the right props since i couldnt find one that had the same power it ended up trun 4300 and i try to never cruise over 3000 rpm and it did 30 mph at 3000rpms i was very happy with it for a 30 footish boat

prowlersfish wrote:as far as your link they are I/O prop sellers ( we are talking inboards) do you belive every thing a salesman tells you ?

I was expecting that response, I don't see why that makes any difference to the overall theory. Different drives and boats will require different dia, pitch and rake changes but those 3 vs 4 advantages often remains. I'm not going to put in any more as you will say those boats are too big!

I now understand that your boat is non standard and hence the bad in water attitude. I could argue that the diesel installation was faulty as it was not in consort with the boat design and maybe a different diesel option should have been used to bring the balance further aft... but I will resist the temptation to say that.

Ready 123 its clear you belive every thing you read on a web site and then its fact to you . some times in the real world thing are not the same as on papers . you also do not unders stand engine loading or how speed can effect fuel burn some of the stuff you have said is correct sometimes . you seem to think becuse you think a prop that feels better then it must be better for eveyone . I/o props have to deal with exhust being run thru them and do not have deel with shaft angles like we do.


now you say you insult my boat but would then you go ahead and do it anyway ??

let me see at over 24 knots the bow stater to get low but its no issuse untill you get above 27 knots and then you get some plow . so you say my engines are in wrong or the wrong engines . boy you know it all don't you ? first you can move them back with out changeing shaft angle and then you end up with other proplems lighter diesels ? no thanks I like low rpm engines .
I dont need trim tabs at cruse do you ? if you do somthing is wrong as your perfict boat needs more lift !

all I know is my boat will cruse faster burn less fuel and ride better then yours all on my wrong no count 3 blade props LOL

I think my engines are the perfect fitt for my boat

and the main reson for the low bow and speed , no weaght in the stern
when the diesels were installed the fuel tanks had to be removed and replaced well the side thanks were replaced and the rear tanks removed . also the diesel genset is lighter the old gas one . I could add tanks back there but why ? I don't burn fuel like your boat ( LOL had to say it ) so I carry all the fuel I need .

lmao ..... hey Kevin, can you pass the pop corn?

prowlersfish wrote:now you say you insult my boat but would then you go ahead and do it anyway ??

There was a smiley there!
I find it amusing how you say that 4 blade does not work for you and blaming the blade science while ignoring that the root cause is that your boat is too boat heavy in the bow, not in line with it's original design. Were your boat correctly balanced you might actually see the benefit of a 4 blade.... that is all I am saying.
You can set your boat up any way you wish.... were it mine and I found that the engine change and tank layout had created this negative weighting I would fix it because my principle outlook (insert boy scout motto???) would be to correct the error in design judgement so that full speed would be available for that possible time when I would want to use it.

You think you know all you say my boat is off bal cuze a f'n 4 blade prop is not the best for it ??? at all normal speeds the bow is not riding high it is ride low LIKE IT SHOULD BE !!!! I DID NOT SAY TO LOW !!! yes near top end it starts to get low so what ? if my boat ran faster it may be a issue . Just like your may if it could run faster .


No boat has perfect trim at all speeds , not even yours mr perfect , thats why they make trim tabs .

why do you think evey boat needs 4 blade props ? some people may not want to lose speed or have hull thats off and that needs lift

you think I should move my engines so I could us 4 blades ? sounds like that what your saying to me . maybe yours should be moved so you can run 3 blades LOL


there is a lot more to props the the number of blades

as far as me getting the benefit of a 4 blade the lost of speed with them is all I need to say no . just not the right prop for me and my boat . and that is a fact.

I think you guys should calm down. There shouldn't be so much bickering and more help. If people can't relax and take or leave suggestions we are in big trouble here. We all love our boats and that should be the ultimate goal no matter what. Relax! Life is too short and we should all get along. "Don't take life too seriously. None of us get out of it alive!"
Wes

Wes you are 100% correct