Add more set back and loose 4mph ?????

**derpid** · 07-31-2017, 12:30 AM

So I recently added 4 more inches of setback to my boat, which gives me a total of 14"(brackets and jackplate combined). Prior to doing so I was able to run 68mph all day and take it to a sketchy 70-72, but it was porpoising like a bastard to get there and I had zero chine walk trimmed way up or down. So, I added more setback to stop the porpoise, which it does. But since adding the bigger brackets I have lost 4mph with the same prop, gained a pretty noticeable chine walk, and I am beyond baffled as to what went wrong. I'm thinking that the added set back is really starting to show the disadvantage to my 25" mid. (Boat is better suited to a 20" mid). Not sure where to start but lookin for ideas.

**derpid** · 07-31-2017, 09:50 AM

Guess I should add the boat is a 92 seaswirl spyder 188. Boat is 19.8' long bow to tip of stern. Looks like an older checkmate but weights about 2100lbs. Pad - Vee style hull. When im fully jacked up the shaft is still below the pad, I haven't measured yet. I'm running fairly mild positive trim compared to before, roughly half as much according to the gauge. If I go anymore the chine walk begins. If I slow down to 45-50mph I can trim all the way up with no sign of chine walk and it carries the bow quite nice.

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**darkdream** · 07-31-2017, 02:46 PM

Normal when you add more setback the water comes up higher so your able to run higher. If you don't go higher the propeller is deeper in the water then before with normal setback and have more drag..
Think the best way is looking for a 20 inch mid.

**FMP** · 07-31-2017, 04:40 PM

Good looking boat.

**transomstand** · 07-31-2017, 05:07 PM

Can't rule out that you may have exceeded the amount of setback the hull wants. More is not always better.

**vnemous** · 07-31-2017, 05:29 PM

You went back 4" so try going up 1" if you can. Watch your temp and water pressure. You might get it back.

**Ted Stryker** · 07-31-2017, 05:34 PM

I agree with the prop is likely getting dunked

**derpid** · 08-01-2017, 03:49 PM

Originally Posted by transomstand

Can't rule out that you may have exceeded the amount of setback the hull wants. More is not always better.

I don't think that ive gone too far with setback, I was seeing a prominent porpoise when I was trimmed up to get to my 68-70mph and it still wasn't carrying the bow sufficiently. its a very bow heavy boat. it carries the nose much better now and feels much more stable and requires far less positive trim.

**derpid** · 08-01-2017, 03:58 PM

Originally Posted by vnemous

You went back 4" so try going up 1" if you can. Watch your temp and water pressure. You might get it back.

right now with the 25" mid I'm jacked all the way up and I am running roughly prop shaft 1" below the pad. I agree higher would be better but I'm maxed out. I'm on the fence as to whether or not to swap to a 20" mid or find a swap/ trade to same or bigger etec with a 20" mid and nose cone. when I had 10" setback spinning a 24p scorpion I could porpoise my way to 68 and I wasn't jacked out yet. ive tried all kinds of trim and height combinations but stil cant exceed 64.

**derpid** · 08-01-2017, 04:03 PM

I think I may have found a contributor to my chine walk this weekend while I was double checking bolts and hardware: noticed my tilt tube bushing has some significant wear and giving me some free play. That combined with the high CG from the 25" mid could be giving me my death wobble.

**GETBOATS** · 08-05-2017, 01:53 PM

You've mentioned "pad bottom" several times, this boat didn't have a pad bottom unless some one added it, they were rounded v at the transom with a fairly deep v running forward, very hard chines meaning they turn down, you might post pictures of the transom from a few angles with motor down. Do you know where zero degrees trim is when running? put a straight edge on the bottom, trim till parallel with anti ventilation plate and mark you gauge accordingly. I remember only one strake to the transom, my guess is you're not getting enough lift back there to get the out side chines clear of the water. stay at it, its all about set up!

**derpid** · 08-05-2017, 05:42 PM

Originally Posted by GETBOATS

You've mentioned "pad bottom" several times, this boat didn't have a pad bottom unless some one added it, they were rounded v at the transom with a fairly deep v running forward, very hard chines meaning they turn down, you might post pictures of the transom from a few angles with motor down. Do you know where zero degrees trim is when running? put a straight edge on the bottom, trim till parallel with anti ventilation plate and mark you gauge accordingly. I remember only one strake to the transom, my guess is you're not getting enough lift back there to get the out side chines clear of the water. stay at it, its all about set up!

Ill have to snap a pick for you, but it does have a flat pad. Bout 4' long and 6" wide. its definitely not a "true pad" as it does not protrude from the hull like say a checkmate or something that was purpose designed for speed. But to answer your question, yes I have found my zero degree position on my gauge (was a lot lower in the sweep than I had anticipated). I cant recall the running length of all my strakes but I think the two that run outside of the keel are full length. pics will clear this up lol. I'm going to try a few things to eliminate any motor wobble this weekend as a contributor to the walk. Its been awhile since I've bled the steering, so that's always potentially an issue. Motor mounts, and like I mentioned tilt tube bushings are worn. so I have a lot to eliminate. I also need to find some counterweight to balance the boat so I can drive through the walk and figure out the happy spot, so sand bag or something cuz the GF absolutely does not like it when I take the boat for a walk lol. I'm sure when I figure it out it will be one of those things everyone on here has gone through in their early days.