What I am trying to do is to determine if I need to change my prop on a replacement outboard. Currently have a billfisher 2008 with a F150 running a 17-M prop. I am changing the motor out to a Honda BF225a(secondhand) which has a 17" x 14 1/4 prop. I think I will have to put it in the water with the 17" x 4 1/4 and do some tests and get some data and then post it up and see what I should use. I think I will be replacing it with a 19" x ? as raging bull ran a 17 x 4 1/4 on his 237 billfisher which is a lot heavy and longer boat

The Suzukis run bigger props due to the offset drive shaft which gives a different gearbox ratio typically we swing one size bigger than other brands for the same hp

Mcboat real good question.

You would think it was much just looking at it but when you take the cowling off the block is quite a way forward inside.

I am picking you probably have about 40kgs more of that weight on top or inside the transom. The block is about half the weight of the whole outboard.

Did you already have an engine as have a DF225 new that can do at quite a good price.

Cheers

FYI, I just brought a buccaneer 720 hard top and fitted a 250 Yamaha 4 stroke which is the late model 4.2l version.   Been having a bit of a mission finding right prop.    Mechanic specified a 19M which is 13 3/4 x 19 (black stainless).   Could only get 5400rpm at WOT and medium load. 42 knots.

Tried a 17M. Same dia but reduced pitch. Topped out at nearly 6000rpm at 39 knots but had a slow cruise so wasn’t happy with that either.

Found another cheap 19M and have had it repitched down by one inch and hopefully that will be right. Haven’t tested it yet.

Interesting thing is the 19M’s turn out to actually measure 18”. Had to check both props to make sure one hadn’t already been repitched.   Must assume the 17m is only about 16 then as I have 500-600 rpm diff between 2” pitch. So my repitched (“technically” 18”) is actually pitched at 17”. Good accuracy there from Yamaha.

These seem like relatively small props compared to what you are talking about so must be some difference in the gear ratios.

Motor seems a real nice fit for the boat though even with 30” shaft. Had the transom lifted and you don’t notice size or weight.

Slapper 61

GH..

i may be a simple man that doesn't use a calculator to set up boats but surely in the absence of an available prop to test,  under $200 for a Permatrim vs $1000 - $1500for a quality, new stainless steel V6 prop that usually deliver same results seems a pretty simple choice?  Even to just try?

Wow, all i was doing was suggesting that there was an alternative to "The Steps way" but apparently this is not possible?

One thing I’d say from my experience buying used motors any one with a permatrim etc fitted I instantly dismiss . Mainly because I’ve never needed one to do what the motors meant to do .
So I would suggest fitting a permatrim will reduce the value of your motor if you eventually sell it .
Just a thought on the subject .
I think Steps is a great asset although not neccasssarily correct on everything.

As i mentioned, not all setups respond favourably to a Permatrim, that i agree are bit of a bandaid, but not all setups perform to potential with merely standard factory prop/engine height changes, regardless of what you may have read.  

If something improves holeshot, enables hull to plane at a lower speed,  increases ride stability while underway, and lower fuel consumption then i (and many people) consider that an improvement, regardless what anyone says.  If that improvement is achieved at a $$$ saving, most people consider that a great improvement, you refer to it as "seat of pants", most call it irrefutable proof.  Put that into a formula/calculation any way you please

Mathematical modelling has its place as a starting baseline but actual performance doesn't lie.  The first flaw with this is how many people actually put their rig across a weigh bridge?

My argument is not strictly pro permatrim but that there are options

I repeat, a permatrim is not the solution for all case's and yes ideally satisfactory results will be meet with standard factory propping/engine height adjustment but they are an affordable, viable option in many instances, despite being bit of an eyesore

You seem pretty hung up on your earlier questions

Iv'e worked for 3 franchised dealerships, had industry standard recognized training from 4 major marine manufactures and handled warranty work/claims for all.  Amongst other work I still occasionally travel to carry out installs on contract in locations where there is not a dealer presence and boats cannot be transported.  Cant say i've come across anyone called crouch Keith or Gerr but while we're name dropping do Yamaha, Mercury, Suzuki and OMC/Bombardier ring a bell? (yeah yeah i know😅😅)

I've never seen any failure as a result of any correctly fitted accessory, including permatrim, therefore i have never seen a warranty claim denied as a result.  And yes i have seen warranty claims on components unrelated to installed permatrim accepted.  To suggest no warranty of any kind on any product due to an accessory fitted is scare mongering, ECU fails? "Sorry no warranty cos you've got an attachment on your gearbox"?  That's laughable.  Cavition plate breaks, well that'd be different but be more about incorrect install i expect

No manufacturer in any industry like accessories being fitted to their product , it implies a shortcoming in their product.  No accessory improves all aspects of a products use, if it did, manufacturer would buy rights/company and make that accessory a standard feature.  It doesn't mean that accessory has no use

I only have one question for you

Tell me what dealerships/brands you've worked for to obtain your obvious extended knowledge?

Or is it a hobby?

Thats all i've got to contribute and wont be posting again on this, apologies to others its become bit of a pi$$ing match

Ps, your not a University lecturer by any chance?