Proping a Scarab, just a little different...

jserb · Feb 10, 2009

I know i know i have seen these threads and they are all vitrually the same thing, however i know you guys like to have max RPM and speed of the boat, however i have never ran these motors and the max speed of the boat is unknown to me.... and i just dont know where to start with propping this 1985 scarab sport. any tips or genrule rules of thumbs when it comes to proping a boat? I have twin 2003 250hp evinrude outboards and i am mounting them on my boat and then need to prop it, i have no clue where to start, and can these outboards run with clever props? Are they more efficant, less efficant, do they really make a different in speed?? are they good for a heavy boat, please help..

Tacklewasher · Feb 10, 2009

Re: Proping a Scarab, just a little different...

Can't believe your looking at props already. You've done a heck of a job on your boat to be at that stage now.

Serious kudos.

Dhadley · Feb 10, 2009

Re: Proping a Scarab, just a little different...

When you mount them make sure to center them on the lifting strakes. We've found that sometimes one strake is further or closer to center than the other one. IE - if you measure out from dead center of the transom one motor, generally the port one, isn't lined up with that strake.

jserb · Feb 12, 2009

Re: Proping a Scarab, just a little different...

Dhadley said:
When you mount them make sure to center them on the lifting strakes. We've found that sometimes one strake is further or closer to center than the other one. IE - if you measure out from dead center of the transom one motor, generally the port one, isn't lined up with that strake.

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I NEED YOUR HELP I BOATERS! i guess B bracket recently went out of business, they are the company that made the bracket i bought for the boat. I need help trying to find out how to mount this bracket to the transom, ex. the height as to where to mount the bracket. please help! its a full swim platform so it will be very easy to mount left to right (it fits from port to starb) but the height is what is getting me. DH i think your giving me a good hint but im posting this to get more of a responce. I dont have the orginal brackets that were on the boat, so i dont know what the height needs to be. I have a water line and thats about it. Its a twin engine mount b bracket and i know someone out thier knows how to mount this. please help!

Dhadley · Feb 13, 2009

Re: Proping a Scarab, just a little different...

I'd guess you probably have the 28" bracket. The general rule of thumb is that for every 5" you go back, you can go up 1". So, if the AV plates are parallel at the transom and you go back 28". you can mount the bracket so the AV plates on the motors are 5-6" up at the mounting location.

If you are going to use a performance type prop, that may be a tad low but you can always go up when mounting the motors to the bracket and or add manual plates later.

It's a shame B Bracket went away, they were good folks.

jserb · Feb 13, 2009

Re: Proping a Scarab, just a little different...

DH Im sorry, I really don?t follow you on this?. I believe (only cuz im at work and not at home to measure) it?s a 32?? set back. What is this 5?? to every 1??, the way I am reading that means that I would mount the bracket 6?? from the bottom of the boat and I know that?s not right?..The ONLY advantage I have here is a guy has the same boat in the city I live in. He has a gil bracket and its mounted; I was thinking of going over their and measuring his set up and then taking those back and mounting mine off of those measurements. I have included a few photos of his boat and a few photos of my OLD brackets and it ?looks? like the height of his brackets were around the same height of my brackets at the time. So my question to you DH is what should I take photo?s of and what exactly should I measure on his boat to get the right location for my bracket? He has a different bracket and different engines, however I assume the location would be ok?..so do you have any thoughts of what I should measure on his boat to get this thing right? He has the same year and make as my scarab. Let me know man.

Dhadley · Feb 13, 2009

Re: Proping a Scarab, just a little different...

What you need to do is imagine the motors mounted on the transom. The AV plate (plate right above the prop) when parallel to the bottom, in the mounting location of each motor (left & right of center) would be even with the hull directly in front of the motor. The plate wouldn't be above the bottom nor below it. Then going back 32", those plates would now be 6" up.

Your bracket may be mounted higher than the single in the picture because a single engine will be mounted in back of the deepest part of the V. Twins will be higher just because of the V going out from center.

Are your motors 25"?

jserb · Feb 16, 2009

Re: Proping a Scarab, just a little different...

DH they are 25'' shafts, i "kind of" get what your saying....basically my AV plate will actually be "higher" than the bottom of the boat(relative to where each motor is mounted 13'' from Center line) @ 32 inches the AV plate should be 6 higher than where the bottom of the hull is???? please help!lol!! i am trying to mount this thing this weekend :-(

Dhadley · Feb 17, 2009

Re: Proping a Scarab, just a little different...

Yes. If the motors were stuck to the transom the AV plate would be no lower than even with the bottom. Going back 32" the plates would now be 5-6" higher.

Don't forget to take into account the transom angle. If it's 90* to the hull bottom when the motors go back they'll go straight back. If the transom has an angle, as the motors go back they'll end up lower.

jserb · Feb 17, 2009

Re: Proping a Scarab, just a little different...

DH wow! it just clicked, much easyer than i thought thank you. Now as for a small simple but fair question for you. My 2003 evinrudes they are 25'' shafts, now with that being said when you say "25''" shafts does that mean 25'' from the first holes on the motor mount? cuz if so, then that means all i need to do it measure up 25'' on my transom ( respective to where each motor falls ofcourse) and then add 6'' so 13'' left and right of my centerline i will go up 31'' and mount the bracket! Does this sound about right to you DH?

Dhadley · Feb 17, 2009

Re: Proping a Scarab, just a little different...

The shaft length is measured from up under the mounting brackets (where the bracket would fit over a transom) down to the AV plate. On a 25" motor a V6 will probably measure about 25 3/4" or so.

jserb · Feb 17, 2009

Re: Proping a Scarab, just a little different...

DH i invite you out on a ride when shes put together! Just to recap (cuz i wanna make SURE i drill these holes right) im bouncin this off of you. With the measurements i have give a 32'' set back, 25'' shafts i should mount my bracket 31'' above bottom of hull where the motors fall.

-just a side note if you look at my photos of the bracket (im sure your aware almost 99 precent of brackets have this) but on the bracket where the motor acctually mounts to the bracket itself actually raises up (lets say cuz im at work and i cant measure 3 to 4'') ABOVE the top part of the bracket, so with that saidddd with my current numbers i will mount the bracket 31'' up PLUS add the 3 or 4 extra inches, or do i subtract these extra inches?????

Dhadley · Feb 17, 2009

Re: Proping a Scarab, just a little different...

Don't forget the transom angle, if there is any. The bracket may or may not have that compensation built in. The way we've always done it was to either hang the motors on the bracket or hang something on the bracket to simulate the AV plate location and set the bracket up against the boat. With a straightedge along the bottom and back to the AV plate you can see where everything should be.

ondarvr · Feb 18, 2009

Re: Proping a Scarab, just a little different...

All measurements should be taken from the top of bracket where the motor is actually bolted to, not where the bracket bolts to the transom.

jserb · Feb 22, 2009

Re: Proping a Scarab, just a little different...

DH this is what it looks like. I took your advice and made a "fake" lower unit out of a 2X4 and then made sure the location of my AV plate was 5'' above the bottom of the hull respective to each motor. This worked out quite well, just thought id show you a few photos of how it turned out. the swim platform is about 5 to 6'' above the water , i think that?s perfect. thanks,

John

BigB9000 · Feb 22, 2009

Re: Proping a Scarab, just a little different...

God I love Scarabs.

Can you maybe zip your rebuild picture collection and email it to me?

(brandonco2@yahoocom)

jserb · Feb 23, 2009

Re: Proping a Scarab, just a little different...

Now how about the proping of these motors with this 1985 hull? I have no idea where to start, what size prop should i use to begin with.

jserb · Feb 23, 2009

Re: Proping a Scarab, just a little different...

Big B, i have like 350 photos i dont think your e mail would hold oall of them

jserb · Feb 23, 2009

Re: Proping a Scarab, just a little different...

DH, unfortunately i have one final question, as of right now i have one bolt in the bracket so it can still be changed with minimal repair. If you look at the attached photo you will see the 2X4 that i used to represent the location of my AV plate, however if you look at how i have attached it to the bracket you can see the 2X4 is drastically pointing in towards the transom. with this said i took the 2x4 and cut it at 25'' (where my AV plate is located) then attached it to the back of the bracket, and then we put the bracket up next to the boat and took our measurements, however now that im looking at it i am questioning if this is ok since the 2X4 is slanted on the bracket (please review photo) i am not sure if your intentions were to have me hold that 2X4 perfectically vertical and make that measurement straight down or not....can you clarify for me how i should mount me "fake lower unit". Also, can you explain to me why the heck outboards are mounted with this slanted bracket? whats the point of slanting them, i thought they sat perfectly vertical in the water???

Dhadley · Feb 23, 2009

Re: Proping a Scarab, just a little different...

That's the negative trim to help get on plane & run at low speed. That looks a little excessive but there are wedges. If your boat was built as an outboard boat the transom had that negative angle built in. If your boat was built out of a stern drive mold the transom could be 90* - no negative angle.

If your boat has the negative angle and that bracket was made to go on a stern drive boat the negative angle would be excessive.

The relationship of the AV plate to the bottom is looked at when the plate is parallel to the running surface of the hull. If the end of the 2x4 was the plate you'd need to trim the motor up some. Then see where you're at. You're probably still close though.

Proping a Scarab, just a little different...

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