Saturn SD470 and Mercury 15HP 4 Stroke Custom Project

[IsmaelPR1]

I bought a 2021 Saturn SD470 a few months back and I've been customizing it since! Also bought a new 2011 Mercury 15hp 4 Stroke new/old stock. Zero hours on it and eith controls. Here is what it looks like at this point. I have had it out twice now for about 6 hours total. Great boat! I keep making tweaks after each time out.

I also had a Harbor Freight HD trailer that I bought earlier this year for motorcycle but I have sold my motorcycle so I converted it into my boat trailer. I am still breaking it the motor but do far so good! I have installed trim tabs and transom hooks to strap it down. All seat boxes were custom made with hinge tops and storage underneath then waterproofed and carpeted. I'm no pro, i just like to tinker and build. Painting the wood on the trailer red. I also extended the tongue a bit with some 2x2 galvanized steel tubing.

 

[Sea Rider]

Welcome to IBoats,

Trim Tabs on a 470 footer powered with a underpowered 15 HP motor ? If the Tabs are set folded downwards will slow the combo down when on its way to plane out. If the purpose is to plane faster what need to do is : Inflate all air chambers to their factory recommended working presure with a pressure gauge, trim the motor to sit at 90 deg (fully vertical) on transom, distribute the deck load evenly and apply full hammer down when revving from a dead stop. If the motor does not sit at the sweet transon height will affect top water performance if both are not well matched. Can check that latter...

If wanting to get the max HP out of said motor must run towards its max 6.1 K wot rpm range factory stated, for that must install an induction tach to check how many rpm is the motor revving at as usually loaded on flat calm water condition. Factory delivered props with underpowered motors for that lenght Sib are usually over pitched....

Happy Boating​

 

[IsmaelPR1]

Welcome to IBoats,

Trim Tabs on a 470 footer powered with a underpowered 15 HP motor ? If the Tabs are set folded downwards will slow the combo down when on its way to plane out. If the purpose is to plane faster what need to do is : Inflate all air chambers to their factory recommended working presure with a pressure gauge, trim the motor to sit at 90 deg (fully vertical) on transom, distribute the deck load evenly and apply full hammer down when revving from a dead stop. If the motor does not sit at the sweet transon height will affect top water performance if both are not well matched. Can check that latter...

If wanting to get the max HP out of said motor must run towards its max 6.1 K wot rpm range factory stated, for that must install an induction tach to check how many rpm is the motor revving at as usually loaded on flat calm water condition. Factory delivered props with underpowered motors for that lenght Sib are usually over pitched....

Happy Boating​

Thanks for the response, truly appreciated. I can get the boat up 20mph with the current setup. I will get a tachometer so that I can fine tune the speed more and get maximum hp.

 

[IsmaelPR1]

Welcome to IBoats,

Trim Tabs on a 470 footer powered with a underpowered 15 HP motor ? If the Tabs are set folded downwards will slow the combo down when on its way to plane out. If the purpose is to plane faster what need to do is : Inflate all air chambers to their factory recommended working presure with a pressure gauge, trim the motor to sit at 90 deg (fully vertical) on transom, distribute the deck load evenly and apply full hammer down when revving from a dead stop. If the motor does not sit at the sweet transon height will affect top water performance if both are not well matched. Can check that latter...

If wanting to get the max HP out of said motor must run towards its max 6.1 K wot rpm range factory stated, for that must install an induction tach to check how many rpm is the motor revving at as usually loaded on flat calm water condition. Factory delivered props with underpowered motors for that lenght Sib are usually over pitched....

Happy Boating​

Would you suggest a different prop? If so which if I may ask?

 

[Sea Rider]

Would you suggest a different prop? If so which if I may ask?

You're welcome, the idea is to get the max HP out cowl rated and increase whenever possible the max fun out of that eye catching combo.

To start with would recommend a Hardline Hour Tach model : HR-8061-2, check Iboats, Amazon. Post a close pic shot from inside deck showing the front motor installation to have a look . Probably will need to install it on the motor's front, the center console sits to way ahead and to route a long signal pick-up wire from the motor to the console's dashboard the induction tach will probably not read accurate ?

What you can do once the signal pick-up wire is installed, the firing sequence properly set and tach attached to other extreme, tape or suspend the tach momentarily at motor's front, note down the idle rpm reading at neutral once the motor is sufficiently warmed up, get a much longer cable of the same gauge, route it well motor to console and check if reads the same ? If Ok, perfect, if not will need to install the tach on the motor's lower pan front.

To know, with trim set at 90 deg, deck load well distributed, with how many souls on board did the combo achieved 20 MPH on flat calm water cond ? Did the motor came with a factory installed prop ? if so should be a 3 blade 10 pitch one, check. Once the max wot rpm read out it's known cam maximize a less pitch, say a 9, 8.5 / 3 blade prop if needed.

Happy Boating

​

 

[mrdrh99]

I'm no help on the motor/tabs situation, but your setup looks very, very nice sir!

 

[SoCalPescador]

First off, very nice boat and mods! You've done great work! I believe what has been recommended is good to start. You want to get max RPM from motors specs. If that's 6000rpm then balance boat for use, full weight of cargo, and see what you can achieve using the trim table you have installed. From there post results. Proping can they be be suggested from this data.