Help with laser bass boat setup

[deerhunter04]

Hi, I have changed my motor which is a 89 Evinrude xp 150 on a 83 laser bass boat. I have a 14x23 raker on it and runs 55 @ 5500. That seems slow for the 150 on it but I could be wrong. I know and also read the other day lasers where designed to run flat. It rides its best with the bow down but with it down it rides so low there's no way to get the speed up. Is there anyone who knows anything about the lasers that can steer me in the right way? Us propeller said if I bring my boat they would try to help. They are a two hour trip one way. I don't mind going but would like some information before I make the trip. I have had people tell me it should run in the high 60s. Thanks for any help I can get.

[Gordon02]

I like the XP/GT 150's - had a White Heat 1986 GT150 myself and ran it for more than 12 years. I also love the Rakers. The XP150 makes power up 5,700, but starts falling after that. 6,000~6,100 is the absolute limit for these due to the heavy-topped pistons (cross-flow) design.

Based on the numbers, your set-up is not optimized and would indicate a very low efficiency number. Propeller efficiency can be calculated and your 55 mph from a 23 at 5,500 comes to about 86%. With careful set-up through documentation and study, you should be able to get that number to 92~93% and in the process - more RPM.
86% efficiency points to a buried prop, excessive over-trim to achieve RPM, and lots of wetted surface due to that trim angle shoving the boat downward. It's the most common set-up mistake made, so it can be fixed! There are several steps to set-up and a hundred opinions - choose carefully. Going to a pro that can drive your boat and give "good" advice can save you money and headaches. Having someone that has spent hours flying a boat on the pad and knows set-up can make the process easier.

My all-time favorite read is the Allison Boat Owners Set-up and Driver Manual -lots of relevant information regarding jackplates, trim, propshaft height, and much, much more.

http://forum.allisonowners.net/index.php?attachments/redbook-pdf.8793/

[FMP]

86 GT150 , small bore 3.5 piston?

[deerhunter04]

The gt's , xp's are crossflow engines and to my knowledge are all 3.5 pistons.

[Gordon02]

DH, I and others had an in-depth discussion about set-back, prop height, and speeds a few weeks ago. I think we covered at least some of what you'll be facing here in 3 pages - Have a look and comment here. I don't want to dampen your enthusiasm, but there are entire books written on this subject so getting everything you'll want to know about set-up won't likely happen in the few post and few pages/drawings offered here.

It will take research, time, and documentation of what worked and what didn't.

https://www.screamandfly.com/showthread.php?334784-Help-picking-a-used-jack-plate

Gordon

[FMP]

Same piston will turn 7000+ in the V4?
Some of this may help you
https://www.screamandfly.com/showthread.php?221930-The-OMC-Cross-Flow-Thread&

[deerhunter04]

I don't want to sound rude. I know that a jacket plate usually around 6" depending on the setback that's build in when the boats is build put the propeller in clean water. It also allows to raise the motor higher than you can by just bolting to the boat but does require a water pressure gauge. I also know it takes time to get one right been there before. I figured I had a prop problem which was the same as the last time when I got the boat. The problem I run into in my area is all bass boats don't rig the same. You might get close you might not. I also know that a properly trimmed boat runs faster. Maybe I should have asked what props seams to run better on the 17.5 laser with the xp 150.

[Gordon02]

FMP, page 182 of the Bass Boat Bible by Earl Bentz states the max of a cross-charged GT150 should be kept to 5,800~6,200 - no more, so I've always kept that lesson.

DH, my Rakers have always performed extremely well. My GT150/178V Astroglass set-up took me over 2 years to get from it's 62 mph dealer delivery to the final 68 mph plateau. Same, exact prop but with a 6" jackplate, water pressure gauge, going with a light-weight trolling motor (12 Volt Sneaker), and putting everything in the rear-most lockers. Weight anywhere forward of the transom kills speed by pushing the hull into the water. Your Laser should be 3~4 mph faster than my heavy, resin saturated Astroglass was - easily. Just adding a 24 or even a 26 Raker won't get you there. You have other restrictions to resolve first - something in set-up is preventing you from turning higher rpm.

I sold my Astroglass in 1996 and kept the GT150 - I liked it that much. In fact, I had my brand new 1997 Allison made with matching colors so the boat would have the same White Heat scheme. Once again, the set-up had to be started from scratch and developed for the all-new conditions. Nothing learned on the Astroglass/GT150 applied. I added Land&Sea solid mounts shown to be required at higher speeds then installed a Bob's LWP just so I could raise the propshaft. Higher propshaft heights meant less vertical leverage so a 12" Allison jackplate was needed on top of the factory off-set to carry the bow at speed. The 24 Raker quickly ran out of pitch and was replaced with a 29" pitch SRX over-hub wheel. After adding composite reeds (Boyensen) -78 mph was they absolute best I could get this Allison/GT150 combination to do. That long Bob's gearcase wasn't needed for blow-out prevention, but it's LWP attribute was likely a good trade-off for drag reduction since the added length of the bullet was probably less than the lower settings for water feed without.

2 years later, I gave up chasing 1~2 mph with the Johnson and just ordered a new Hi-Perf 2.5L Short Shaft from Mercury Racing. You guessed it - all new set-up required. New Jackplate, new prop, and lots of seat time to learn to manage the 90mph out of the box. A few months later and the heads came off and sent to JSRE for blueprinting and 35cc chambers......30" Chopper II made by Mercury Racing specifically for this Allison and 96.2 mph. Set-up is everything!

Gordon

406769

[FMP]

No harm in keeping it happy for years of worry free use. Just showing some examples of mods from one of the best OMC guys ever, ever.

[deerhunter04]

I know there's guys here that are way more knowledgeable than I am. I know most guys run racker style props. I can't say that my previous setup was to 100% but with the smaller engine turning 5800@52 with a silhouette 13 1/4x21 ss prop. I set the new motor to the same hight but it doesn't seem to plane has high and it only gained 3 mph. I plan to raise the motor 1/4 and try tomorrow. Us propeller told me that the 89 xp had a problem with not reving pass 5600 does anyone know if that is true? I tried a 4 14x25 blade last year and it was slow to get up and ran about the same. Sometimes I wish I had a nitro or statos because the lasers are slowly disappearing