You are right that lilac will grow faster than arborvitae. But they don't have the masking effect in the winter either, which, I would assume, will be the boat's primary storage time for the year.

All options are plausible. But as with any combination of deciduous and evergreen plant materials, you must remember the inevitable as they begin to grow together: the "bare spots" of the evergreens that are covered by deciduous materials in the summer, are suddenly exposed when leaves drop in the fall. Holes, or empty sides of your evergeens might not look too inviting, even though it is a healthy, natural and normal consequence.

Unfortunately the boat/trailer is there year round. So I'm looking for something that will grown fast and block it out.
I've put a lot of work into my garden so having an eye sore parked behind it certainly isn't appealing. Plus that's one of the first things we see as we walk out our front door. There were large shrubs in this area when I put my garden in years ago. I guess I'll have to see if someone else has an idea.

This evergreen list is from the U of MN Extension Service - might be something here worth looking into for your screening requirements:

Trade Name of Evergreen/ Hardiness Zone/ Growth Rate/ Maximum Size (feet)/ Shape/ Light Requirements
Arborvitae
Emerald 3 Med 15 Cone Full Sun - Full Shade
Globe 3 Slow - Med 5 Globe Full Sun - Full Shade
Techny 3 Slow - Med 15 Pyramid Full Sun - Full Shade
Firs
Douglas fir (not a true fir) 4 Med 60 Pyramid Full Sun
Balsam 3 Slow 50 Pyramid Full Sun - Part Shade
White 4 Slow - Med 50 Pyramid Full Sun
Hemlocks
Canada 3b Med 40 Pyramid Part Shade - Full Shade
Junipers
Savin 3 Slow 5X10 Spreading Full Sun - Part Shade
Green Globe 4 Med 4X4 Globe Part Sun
Rocky Mountain 3b Slow 15X8 Cone Full Sun
Wilton Carpet 4 Slow - Med 2X8 Spreading Full Sun - Part Sun
Prince of Wales 4 Slow - Med 4X8 Spreading Full Sun - Part Sun
Pfitzer 4 Slow - Med 4X6 Large Spreading Full Sun - Part Shade
Sargent 4 Slow - Med 2X8 Spreading Full Sun - Part Shade
Pines
Austrian 3b Med 60 Pyramid Full Sun
Mugo 3 Slow 10 Globe Full Sun
Ponderosa 3 Med 60 Pyramid Full Sun
Red 2 Med 60 Pyramid Full Sun
Scotch 3 Slow - Med 50 Pyramid Full Sun
White 3 Med 60 Pyramid Full Sun - Part Sun
Spruce
Black Hills 2 Slow 40 Pyramid Full Sun
Norway 3b Med - Fast 60 Pyramid Full Sun - Part Sun
Yews
Japanese Spreading 4 Slow 5X6 Large Spreading Part Shade - Full Shade
Japanese Dwarf 4 Slow 3X5 Large Spreading Part Shade - Full Shade
Taunton Spreading 4 Slow 3X5 Large Spreading Full Sun - Full Shade

The area is 30 long, how much width do you have to work with?

Helen.

The arborvitaes are planted in wooden raised beds that are about 3 feet wide. The garden it's self is about 15 feet wide x 30 feet long, so I have some room to work with. It also sits on a slight slope. I'm leaning towards adding another raised bed in front of this one and moving the arborvitae to the new front raised bed because they grown slower than lilac. Then I would plant some lilacs and maybe a few small trees to the to back bed.It's a lot of work but, I believe that it will be well worth the effort once I'm done.What do you think? This was my hosta garden at one time but,I'm really tired of looking at the boat (plus this neighbor is very nosey) so I've decided to just turn it into a shrub garden. I just want my peace and privacy.

Sounds like you have some nice space to work in, which allows you more options. A mixed shrub border would not only provide a screen but give you alot of interest as well. If it were mine, depending on the amount of slope, I think I would ditch the raised beds, ammend the soil and come up with a nice grade, and then use a variety of trees and shrubs along the property line. Often times, solid lines of one specimen look like a wall of plants, and when one plant goes bad, the whole wall looks bad, it does not have to look like you are hiding something, you simply give yourself something better to look at. If the shrub/tree border is successful, even if there is a hint of boat or trailer in sight, you won't notice so much because the border will be dominant. There are so many things to play with here, it is really exciting. You can pop in small flowering crabs, things with fall color, shrubs with summer flowers, you can even toss in a perennial or two. Play with height and texture, evergreen and deciduous. You do not have to abandon your arborvitae either, just use them in groups of 3 or so, the evergreen is an important component because it gives you winter color. Make this project a gardening adventure, not a chore, and you will have more than privacy and peace at the end. Well thats my 2 cents anyway, more like 20...I do run on when it is March and -1 degrees outside.....Helen.